The TARDIS lands in the intersection of two runways at Gatwick Airport. Aeroplanes buzz low overhead and Jamie, first out, is frightened at what he calls "flying beasties". He has never seen such a thing before. The Doctor is next out and spots one plane in particular that is a problem - it is trying to land on one of the runways and will crash into them. Jamie and the Doctor run for cover, Ben and Polly following quickly after. Luckily, the pilot of the plane sees the obstruction and manages to pull into a steep climb to avoid it and the people.

A policeman patrolling nearby spots the strange people walking about on the tarmac and shouts at them to stop. They do the opposite as the Doctor orders them all to scatter. Ben stumbles as he goes and the police officer gives chase, figuring he has the best chance of catching the young man. The others get away.

In air traffic control, the Commandant of the airport is receiving news of the obstruction on the runway. One of his air traffic controllers, Meadows, reports that the pilot of the affected plan believes the obstruction to be a police box. The Commandant, a no-nonsense man with a short fuse, does not believe this. He sends the plane back into stack to await further clearance and he has his secretary, Jean Rock, get the police on the line. He wants the obstruction found and cleared immediately.

The police hurry to the intersection of the two runways and find the TARDIS. They waste no time in loading it on a lorry and driving it off. The hunt is intensified for the people seen running away from the box. Ben has found a hiding place among some outbuildings just off the tarmac. He stays put as the police nose around.

The Doctor and Jamie have found hiding places near one another, behind the enormous wheels of a parked aircraft. They remain hidden as the police zoom about in their search. Both are wondering what has happened to their friends.

Polly, too, has made her way to some outbuildings. They are hangars and offices for some of the smaller airline carriers at the airport. She moves cautiously among them until she spots a policeman approaching. She is forced to duck into the nearest door for cover. The sign on it says Chameleon Tours.

She finds herself in a storeroom/office full of crates and equipment. It is gloomy and grimy. Polly does not get far inside when she is stopped by the sound of raised voices. She ducks down behind a crate as two men emerge from an upstairs office. The first carries a large envelope and seems headed for the exit. The second is wearing an airline pilot's uniform and calls out to stop the first man. When he does not stop, the pilot removes a strange looking pistol from his coat pocket, calling out a more urgent warning.

The man stops and turns. Seeing the gun, he attempts to run but the pilot fires. A strange humming noise issues from the gun and the man falls dead to the floor. The pilot snatches back the envelope from the body and tosses a dirty blanket over the man before heading back upstairs into the office.

The pilot enters the small office and goes directly to a shelf containing tins and supplies. He activates a hidden switch and the shelf slides back into the wall. Inside is a much larger office, containing monitor screens and some very futuristic looking controls. He activates a control and one of the screens comes to life. On it is the face of another Chameleon Tours pilot, obviously a superior to the first man. The pilot in the hangar reports "trouble" and that "someone found the postcards". The other man will be there momentarily.

Suddenly an alarm blares in the little office and another monitor activates. It shows activity in the hangar as Polly emerges from hiding to examine the body of the dead man. The pilot rushes out of the office to confront her but Polly hears him coming and races for the door, knowing what will happen if she's not successful. Polly races out onto the tarmac and the pilot follows. He draws his strange-looking gun and levels it at her but is forced to break off and return to the hangar when a police motorcycle drives by. Polly is safe... for the moment.

Elsewhere, Ben is still free, hanging close to the out buildings. He sees a lorry driving past with the TARDIS loaded on the back, escorted by police motorcycles. He watches as the "obstruction" is dumped behind a hangar.

In air traffic control, the Commandant receives a report of this activity. He is glad that the obstruction has been cleared from the runway and orders his air traffic controllers to begin bringing planes down again, but he still does not know why there was a police box on the runway. He calls up the police chief, Superintendent Reynolds, and crossly tells him to find out what happened and why. Reynolds does tell him that four people were seen running from the police box but that none of them has been caught as yet.

Not satisfied with this answer, the Commandant places a call to all immigration stations to beware of suspicious characters trying to enter the airport.

Jamie and the Doctor continue to hide behind the aeroplane tyres, waiting for a safe moment to emerge. As they watch, they see Polly running across the tarmac and call to her. She joins them, needing a moment to get her breath back. When she does, she immediately tells them of the murder she witnessed. Unfortunately, the Doctor is determined to investigate, which means that Polly will have to lead them back to the hangar. She is frightened and nervous, not really wanting to go back. She also misses Ben who is nowhere to be seen. Jamie assures her that he and the Doctor will look after her and that they will find Ben...after they investigate that hangar.

The Chameleon Tours pilot returns to the hangar to find his superior already there, standing over the body of the dead man. The superior is called Captain Blade. He is matter-of-fact and clearly in command. His subordinate, Spencer, has no answer to the questions Blade asks and tries to explain that he had no choice but to kill the man. Blade is beyond that, wanting to know who the dead man is. A quick search of his pockets produces an ID - Detective Inspector Gascoigne. A policeman.

Spencer is worried that "a parent" sent the inspector, but Blade thinks that irrelevant at the moment. Most important is a quick disposal of the body. Spencer hurries to the hidden inner office to make arrangements. By the time Blade joins him, the arrangements are made. Spencer also destroys the inspector's identification and several suitcases which remain on the floor in the office. He uses a high-tech machine set into one wall that sounds very like a shredder, although very advanced. Apparently the inspector interrupted Spencer while he was destroying the suitcases initially. Spencer moves nervously under Blade's cold eye.

An alarm sounds in the office once again and the monitor activates. It shows the Doctor, Jamie and Polly entering the hangar. The Doctor goes straight to the office door upstairs. It is locked and no one can be seen inside. The Doctor was hoping to find the killer at home but Polly assures him that she will recognise the man the next time she sees him. Blade overhears all of this, becoming more disgusted at Spencer.

The Doctor goes to examine the body and is very concerned. All the signs clearly indicate that the man was electrocuted, even though Polly says what she saw was a gun. The Doctor can only conclude that it is a type of gun not yet developed on this planet.

Blade overhears this and is intrigued. This Doctor has knowledge greater than most humans and is a threat to their "operation". There is a clear intimation that Blade and Spencer are somehow better than humans. Spencer offers to kill the Doctor to even the score, but Blade thinks they should concentrate on Polly as she can identify him. The Doctor is of little account at the moment, despite his knowledge. No one will believe what he says, even if he is correct.

The Doctor has seen enough and decides that they must report this murder to someone in authority. Polly is worried about leaving the body here but the Doctor knows they can do nothing for him at the moment. All three of them head for the main airport building.

However, Spencer intercepts them on their way. He hangs back in the shadows of a doorway while the Doctor and Jamie pass by. When Polly approaches, Spencer grabs her around the neck and points a silver, pen-like device at her head. She freezes into immobility and Spencer drags her away easily.

The Doctor and Jamie do not for the moment notice the loss of their friend.

Polly comes to a few moments later back in the hangar. Spencer tells her that he temporarily disabled her with his device and that she will be back to normal in a moment. He drags her up the stairs and into the inner office.

Spencer is glad to have redeemed himself by kidnapping Polly, but Blade still has some questions. Polly is defiant, calling them murderers and reminding them that her friends will be back soon. Blade assumes that she must work for one of the airlines to have been in this part of the airport but Polly does not understand what he is asking. She answers honestly that she and her friends were just lost and Blade seems to believe her as he breaks off questioning her.

The alarm in the little office goes off again as Jamie and the Doctor return. They go again to the office door, but it is locked and empty.

Polly sees them on the monitor and makes a dash for the hidden door, trying to find a way to open it or let her friends know she is back there. She cannot be heard and Spencer grabs her and returns her to her chair. She watches helplessly on the monitor as the Doctor decides there is nothing they can do for her here. They must find the authorities and get some help.

Blade watches them leave but he is not convinced this is the last he's heard of them. He says cryptically that he must do something to stop Polly's friends from worrying about her...

The Doctor and Jamie find their way into the main terminal of the airport, following a group of passengers deplaning on the tarmac. However, they must get past an immigration desk first. The man behind the desk is called Jenkins and he is an efficient and officious public servant. The Doctor and Jamie push past the queue and ask to speak to someone in authority. Jenkins calmly finishes dealing with the passenger at hand before addressing the newcomers. He asks the first question he always asks: passport please?

The Doctor tries to short circuit this in order to make an urgent report, but Jenkins stands his bureaucratic ground. Neither Jamie nor the Doctor are quite sure what a passport is and so get to the point, hoping to get a quick response from the man: they've seen a dead body outside. Jenkins smoothly informs the agitated Doctor that he should speak to the police about that. There's bound to be one in the main concourse.

Of course, they'll have to produce their passports before he can let them go in.

The Doctor says they don't have passports and Jenkins thinks that very unlikely indeed. He assumes they are passengers from the same flight as the other people in line, from Madrid. Jamie decides to tell him about the TARDIS. The Doctor stomps on his foot to shut him up but it's too late. Looking at these two strange men, Jenkins remembers the recent bulletin he received from the Commandant. He asks if they know anything about a police box. Once again, Jamie chimes in with an affirmative, only to get an elbow in the ribs from the Doctor.

Jenkins realises he's got two of the people wanted in connection with the police box incident and phones the Commandant immediately, assuring the unsuspecting Doctor that he'll have plenty of opportunity to "speak to someone in authority" very soon.

Back outside, Ben is still hiding to avoid the police. He has reached the hangar area and looks for a place to conceal himself. Unfortunately, he too chooses the Chameleon Tours hangar. Inside, Captain Blade is pounding some nails into a large wooden packing case, sealing it. As he finishes, he goes up to the office and disappears inside.

Ben enters, calling out to see if there's anyone about. He sees no one but continues inside. He is startled by a voice coming from behind him. It is Jean Rock, the Commandant's secretary. She is looking for Captain Blade and barely gives Ben a second look.

Blade comes down and takes the approved flight schedules she is returning to him. Then she is off, ever efficient. Blade then turns his cold-eyed attention toward Ben. He is angry at this apparent trespasser, especially given the previous events. Ben poses as a new employee of the airport and says he just got lost. He's only looking for a way out. Blade seems to consider this for some time before deciding that he will show Ben the way back to the main airport building.

Back at Immigration Desk 5, the Commandant has heard the Doctor's story of murder and kidnapping and is finding it all a bit hard to swallow, especially from the two odd-looking men. Jamie makes matters worse by honestly reporting that the man Polly saw was killed by electrocution from a ray gun. Now she's vanished! The Commandant can only conclude that this is some sort of joke and seems unlikely to do anything about it. The Doctor, quickly sizing the man up, challenges his authority in the airport and suggests he'll need to find someone who can really investigate this murder. The Commandant rises to the implied challenge and orders the Doctor to take him to the Chameleon Tours hangar immediately.

Jenkins is left to phone in the Commandant's whereabouts to air traffic control, along with the quest for the dead body. He is sure it's going to be "one of those days".

In the hidden inner office, Blade is at work on a stack of postcards, attaching stamps to them. They appear to have scenes of Paris on them. Spencer arrives announcing that Polly is being "processed" and that there's room for her on the next Chameleon flight. Where she is going is anyone's guess.

In response to this, Captain Blade rises and opens a large metallic cabinet that sits in one corner of the office. From inside, an arm flops loosely out. It is blobby and mottled, ending in what seems to be an unfinished hand. All the digits are enlarged and knobby, featureless. The arm is attached to a creature inside the cabinet which remains unseen. Blade is unfazed by this creature, producing a syringe and injecting the creature's arm with a clear fluid. Then he pushes the arm up and closes the cabinet door.

Just as he finishes, the intruder alarm goes off again. On the monitor is the Doctor, Jamie and the Commandant. They go immediately to the spot in the storeroom where the body was left. It is of course not there. The Doctor knows that the Commandant's trust in him is very small at the moment; any more setbacks and he and Jamie could easily be facing a charge. He quickly investigates the area where the body was, looking for any evidence to prove his story.

The Commandant becomes more sarcastic by the moment, certain he is looking at a madman. The Doctor admits that there was no identification on the body when he found it. The only thing in his pocket was a postage stamp. The Commandant becomes angry, thinking that this is no evidence of anything at all. The Doctor points out that it is a Spanish stamp, unused, which to him is a significant clue. The Doctor also produces burnt fibres from the area on the floor where the body was. Jamie finds a burn mark on the side of a packing case which is new. The Doctor becomes absorbed in studying it while the Commandant becomes more exasperated by the second. When the Doctor announces that the burn mark was made by a ray gun, the Commandant comes unglued and orders both of them out.

But the Doctor continues putting together the scant clues and the Commandant is powerless to stop him. The Doctor realises that the missing body must have been put into a packing case of some sort to be disposed of. Jamie finds just the thing in a corner and they go to it, trying to prize open the lid.

Captain Blade finally emerges from the office, having watched all this on the monitor, and asks if he can help. The Commandant sheepishly asks if they can look inside the case, not entirely sure why he's allowed the Doctor to rope him in this far. Blade thinks about protesting but when he learns that this man is the Commandant, he changes his mind and even produces a crowbar to open the case. Blade plays it cool as he does so.

The lid comes off to reveal... a case full of plastic cups. The Commandant is livid and will listen to no more of the Doctor's foolishness. He orders them out, offering an embarrassed thanks to Blade, and assuring the Doctor and Jamie that he's going to find out who they are and why they're here. His tone is resolute and the Doctor decides not to protest. He and Jamie go out.

Blade waits until they are all gone before calling to Spencer in the office. He emerges a moment later, supporting another person/creature/something by the arm. It is humanoid but just barely, its figure concealed by a long overcoat, a hat pulled low and a scarf. Blade joins in and helps the thing down the stairs. It moves with great difficulty as if ill or drugged or unused to such movement. The thing stumbles at the bottom of the stairs but Blade and Spencer steady it. Its hand is the same as that in the cabinet in the office - knobbly and featureless.

Spencer is concerned that the thing might not survive but Blade thinks he will. "He" is nearing something called suffocation point. They must hurry to get him to the main airport building before it's too late.

Back at Immigration Desk 5, the Doctor and Jamie are forced to sit down. The Doctor tries protesting again about what they saw, but the Commandant shuts him down efficiently. He orders Jenkins to get Superintendent Reynolds to get these trespassers off his hands, but Jenkins has another flight of passengers to deal with. The Commandant starts to make the call while Jenkins addresses the queue of passengers.

Jamie looks at the group and reacts with excitement. He draws the Doctor's attention to one particular person: Polly! She is in line with the other passengers. Both Jamie and the Doctor are happy to see her alive and well.

Spencer and Blade make their way slowly across the tarmac and into the airport. It is a long journey that is clearly becoming more difficult for the thing they are assisting. The crowds milling about notice nothing out of the ordinary.

The Doctor interrupts the Commandant's call to point out Polly to him. She has just reached the immigration desk. However, the girl seems puzzled. She says she does not recognise the Doctor and Jamie and does not respond to the name "Polly". To the Doctor's astonishment, she says she's never seen him or Jamie before in her life!

Spencer and Blade finally reach their destination - the medical centre in the airport. There is no one on duty but they are not looking for anyone. They help manoeuvre the creature to sit on an examination table. Then Blade removes the cap and scarf from its head.

Back at Immigration, the woman who looks like Polly continues to insist that she has never seen the Doctor and Jamie before. She says her name is Michelle Leuppi and that she is from Zurich, just arrived in England to work. She has a passport and a work permit that back up what she says. The Doctor and Jamie are astonished and try to trip her up regarding her English accent. She smoothly rebuffs them. The Commandant has heard enough and sends the girl on her way, much to the dismay of Jamie and the Doctor.

The Commandant has had it up to his eyeballs with these two jokers. He refuses to listen to their story of a dead body and ray guns and a woman who doesn't even know who they are. He calls Superintendent Reynolds, ready to turn them both over to the police. The Doctor realises what is happening and directs Jamie to flee into the airport. The Commandant takes this in his stride, calmly explaining to Reynolds that they've run off. He passes on a description, confident the fugitives will be caught.

In the medical unit, Blade and Spencer run through some medical procedures on the blobby, misshapen alien creature that lies on the table before them. We can now see that it has no features on its face, like an unfinished store mannequin. Its breathing is laboured and the two men are clearly concerned. A woman in a nurse's uniform arrives, completely unfazed by the sight before her. In fact, she chastises Blade for being 20 minutes late in arriving. Her name is Nurse Pinto and she is very much in charge here.

She swings into action immediately. She wheels in another body on another table. This is clearly a human, an air traffic controller called Meadows. He is unconscious and clearly part of whatever operation is going on. Pinto removes two arm bands from a nearby storage cupboard - one white, which is placed around Meadows' arm, and one black, which is placed around the creature's arm. She then wheels in a large machine that looks similar to an X-ray machine and places it between the two tables. She connects cables from the machine to each of the two arm bands and switches the machine on.

Meadows' body twitches and jerks on its table under the influence of the machine. In opposition, the laboured breathing of the alien creature settles and it relaxes on its table. Suddenly its blank features begin to change and take on human shape. Eyes, nose, mouth, ears. They all begin to form, changing the alien into a human. A specific human. Meadows.

Elsewhere in the main airport building, the police search for the Doctor and Jamie, having a difficult time finding them amongst the sea of travellers arriving and departing. They also miss another fugitive on their list - Ben. He hides inside a photo booth as two policemen pass, glad to still be free.

Jamie and the Doctor sit in the main concourse, hidden behind newspapers as the two policemen pass by. They must continue to evade the police until they can find more proof of their story. Without Polly, they have very little to go on. The Doctor fears that the woman they saw wasn't Polly, no matter how much she looked like her. Jamie finds this hard to believe, but the Doctor assures him that things are not always as they appear.

They are forced to hide again as the policemen pass by again. Luckily they do not notice the two men "reading" their papers. To Jamie's surprise, though, the Doctor is actually reading his. He notices an advert for "Chameleon Youth Tours", budget tours for young people between 18 and 25. He remembers that Chameleon Tours is the hangar where the murder took place and wonders if the name Chameleon may refer to more than just the lizard emblem on the door. His mind is working on the question of why the murdered man might have been killed and especially the nature of his death. There's definitely something strange going on with Chameleon Tours.

Ben spots his two friends across the concourse and races over to them. Their reunion is brief but joyous. Ben is concerned to see that Polly is not with them and wants to know what has happened. The Doctor fears that they are too exposed where they are and wants to find someplace to hide. Ben says he knows just the place.

In the medical unit, there are now two complete versions of Meadows. One is unconscious, ashen-faced and immobile. The other sits up and undergoes a short physical exam from Nurse Pinto. She checks his reflexes and his eyes, both of which are functioning perfectly. However, his voice takes some work to get right. By manipulating a dial on the black arm band he wears, Blade is able to perfect the creature's vocal control until it is speaking just like Meadows.

Finally, there is the memory test. The false Meadows is given a file of information on the real man. It reads the material quickly and is able to repeat Meadows' name, job, and address in every detail. Blade is very pleased. A perfect transformation of alien to human. Again...

Ben, Jamie, and the Doctor cruise the concourse, actually hiding in plain sight for the moment. They walk slowly as they talk. Ben has been brought up to speed and they are trying to decide what to do next. Ben is surprised to spot Polly in a nearby kiosk, working behind a counter. The Doctor is not surprised to discover she is working for Chameleon Tours. The Doctor approaches the girl, "Michelle", and tries to speak to her.

He operates on the assumption that Polly has been brainwashed into forgetting her friends and even who she is and he tries to remind her of the hangar and something she saw there. Michelle denies all of this, getting more and more annoyed. Finally, she blurts out that if she'd seen a murder she would have gone to the police at once! However, the Doctor has never mentioned a murder to her. He has tripped her up and she knows it. Michelle sobs at the harassment and begs to be left alone.

The Doctor leaves her and returns to Ben and Jamie. Ben is particularly perturbed by what has happened to Polly. The Doctor has no answers yet, but he means to find out. They head off to find that place where they can talk.

Behind the kiosk is a small office. There sits Captain Blade, watching Michelle on the monitor. He has seen and heard all that just happened and he calls her back to the office. Blade tells her that the "assignment" he had for her must now be cancelled as "circumstances" are against her. He decides that she must "leave on the next flight" and go back to "base". Michelle accepts this order somewhat sadly, feeling somehow she failed Blade. But Blade blames the Doctor - a very persistent man whom he plans to deal with very soon...

Meadows, now fully established as a human, returns to his work at air traffic control, calmly and quietly taking his seat before his console. Everything seems normal as far as the Commandant's staff is concerned.

The Commandant himself has a visitor at his desk, a tall Scot in a dark suit, quiet and deliberate and resolute. He is Detective Inspector Crossland. The Commandant replies in the negative to Crossland's inquiries but directs him to his secretary, Miss Rock, to follow up. Jean provides Crossland with an airport pass to help him get around the place. Crossland says he was supposed to meet a colleague here at the airport, Detective Inspector Gascoigne, but no one seems to have seen him. He tells Jean that he and Crossland are here for the same purpose - following up a missing persons report regarding Chameleon Tours.

Ben has taken the Doctor and Jamie back to his photo booth hiding place. The three of them are jammed inside the small cubicle. Jamie is curious as to the nature of the machine, but they have more important things to discuss. The Doctor is puzzled about this woman who looks like Polly but says she isn't. He's sure it's not brainwashing but feels that she both is and isn't Polly.

The group is forced to break off as the curtain on the booth is pulled back by someone wanting their own photo taken. They put on big grins and act as if they are posing for their photos. When they are alone again, the Doctor talks quickly. They need to find out more about Chameleon Youth Tours but they can hardly move in the airport with the police looking for them.

Ben reasons that they are not looking specifically for him and he thinks he can have a freer hand to move around. The Doctor agrees and so directs him to the Chameleon hangar to investigate. The Doctor decides to try and see the Commandant again, hoping to convince him of the truth of their story. Jamie is to stay near the Chameleon Tours kiosk and keep an eye on Polly. The three men leave the booth and go their separate ways.

There is more activity at the kiosk as Michelle is approached by a petite, dark-haired young woman. Her name is Samantha Briggs and she speaks with a Liverpudlian accent as she inquires about her brother Brian. She tells Michelle that Brian went on a Chameleon Tour to Rome and has now disappeared. In fact, the hotel he was supposed to have been booked into - by Chameleon - doesn't even exist. Michelle seems unfazed by all this information, trying to tell Samantha that she must have made a mistake. However, the nervy girl has been very thorough, going so far as to contact the police in Rome. There is no sign of Brian Briggs anywhere in the city, despite the fact that she received a postcard from him posted in Rome.

Samantha will not accept any of Michelle's explanations, becoming angrier at the insinuation that Brian may just have gone off on his own and that Chameleon bears no responsibility for him. The police have been little help and she insists that Michelle do something. Michelle calmly agrees to make some inquiries and makes her way to the office at the back of the kiosk.

She uses the communications equipment to try and reach Captain Blade but only succeeds in finding Spencer. She tells him what has happened and leaves a message for Blade. Michelle then returns to the front and gives her apologies to Samantha. The girl marches over to a bench opposite the kiosk to wait, keeping her eyes glued on Michelle.

Sitting at the far end of the bench, Jamie lowers his newspaper and speaks to her, having arrived in time to overhear most of her conversation with Michelle. He says he may have some information and offers to help. Samantha is certain that her brother is all right - he can take care of himself - but she just wants some acknowledgement from Chameleon Tours of what happened. She wants an answer. Jamie says he wants her to talk with the Doctor. Samantha seems glad of the help but concerned about this stranger when he suddenly disappears behind his newspaper again as a policeman walks past.

In air traffic control, Jean Rock reluctantly approaches the Commandant with the news that someone is here to see him...about a dead body. The Doctor enters, trying to be pleasant and presentable, but the Commandant has already picked up the phone and dialed for the police. The Doctor tries desperately to explain what he saw, pulling out all the stops by telling him that more lives may be in danger. The Commandant will hear none of it. However, Jean overhears the Doctor's story and reacts when he mentions Chameleon Tours. She tries to explain that Inspector Crossland was investigating Chameleon Tours but the Commandant cuts her off as the police arrive.

When the policemen move to arrest the Doctor, he suddenly produces a small device from his pocket and threatens to blow up air traffic control. As expected, the police back off and the Doctor backs toward the door. This is certainly not how he intended to handle this situation but he knows he must remain free if he is to do any good here at all. At the door, he lobs the device at the Commandant and runs. The "device" is a rubber ball.

The police race out after the Doctor.

Meanwhile, Blade has contacted Michelle and provided her with details of how she should respond to Samantha. After she's gotten rid of her, Michelle is to close the kiosk and board the next Chameleon flight.

However, the "information" Michelle provides is particularly unhelpful. She "confirms" that Brian got on the plane to Rome but that Chameleon lost track of him as soon as he landed. The fiery Samantha does not accept this and demands more help. Michelle coldly tells her to return to Liverpool and wait for her brother to turn up then closes the shutters on the kiosk.

Samantha storms back to Jamie on the bench, fuming that the airline couldn't care less about her brother. The determination in her eyes is stronger than ever.

Ben reaches the Chameleon Tours hangar without incident. Going inside, he finds the place deserted, but there are signs of activity. Several metal cabinets sit in the storage area that weren't here before. He tries first one and then another until he finds one whose lid is not completely sealed. Opening it, he is horrified to find Polly inside. She is unconscious, unmoving and cold to the touch. She wears a white arm band on one arm and he fears that she may be dead.

Panicked, Ben races up to the office and to the phone there. He calls for the Commandant at air traffic control, hoping to find the Doctor still there.

But the Doctor has long left air traffic control. He returns to the Chameleon Tours kiosk to find Jamie still waiting. Jamie tries to introduce him to Samantha but the Doctor's attention is drawn by the kiosk. It is closed and Polly is nowhere to be seen. Jamie says she must still be inside as they've not seen her leave. Worried, the Doctor goes to investigate. He breaks into the kiosk and finds - as no surprise - that it is empty. Michelle/Polly is gone through a rear exit. He enters the small office there and looks around.

His first find is a stack of blank postcards from various countries; next he finds sheets of unused stamps from corresponding countries, similar to what he found on the dead man in the Chameleon Tours hangar. Soon his attention is drawn by a monitor above the desk. It is active and showing a view of the main concourse, directed at nothing in particular. Probably monitoring a security camera. However, he stumbles upon the controls to change the view and something interesting happens. The scene on the monitor changes.

First it shows a view of some kind of first aid centre, a nurse checking over equipment. Another change and the monitor shows Ben in the Chameleon Tours office talking on the phone. There is sound as well and the Doctor can hear Ben speaking to air traffic control. He has learned that the Doctor is no longer there and is becoming frantic. The Doctor watches helplessly as Ben is attacked from behind by an unseen assailant. A silver device, something like a fountain pen, is pressed to his neck and Ben freezes into immobility. He is a prisoner of Chameleon Tours.

The Doctor calls out to Ben, unable to make himself heard. He works at the controls on the communications equipment, trying to get through to his friend.

In the office, Spencer grabs the phone from Ben's frozen hand and hangs it up. He tries to remove Ben from the chair in which he sits when the Doctor's voice suddenly comes through the speakers calling for Ben. Spencer opens the secret door and enters the inner office. His monitors there show the Chameleon kiosk and the Doctor inside. Blade arrives at this moment and takes in the situation. They both realise that Ben is another of the Doctor's friends and they are certain that he will come here momentarily. They must hurry.

Spencer drags Ben out of the office while Blade produces a wheelchair. Ben begins to unfreeze as they put him in the chair. Once there, Spencer zaps him again with the freeze device and Ben stops moving, frozen in a sitting position.

Inspector Crossland's investigations have progressed to Immigration Desk 5 and Officer Jenkins. He is showing the young man a photograph. It is Brian Briggs. Crossland and Gascoigne are following up on Samantha's complaint. Unfortunately, Jenkins does not recognise the young man in the photo. Crossland shows him another photo, one of Inspector Gascoigne. Jenkins does remember him from earlier in the day. He had a pass to go outside onto airport grounds, but he hasn't seen the man come back.

Jenkins wonders if perhaps he could have slipped through during a bit of bother with the two strange men and their story of a dead body. Crossland listens to the story seriously, despite Jenkins' obvious disbelief. Jenkins describes the two men in question and how they ran off into the airport. Crossland wonders if these men might not be connected to Gascoigne's disappearance.

Back at the Chameleon Tours kiosk, Jamie and Samantha cool their heels waiting for the Doctor. He has left the kiosk on a mission, telling them very little but asking them to stay put for at least 30 minutes before coming to look for him at the hangar. The agony of waiting is wearing on them, particularly Samantha. She can respect the Doctor's obvious intelligence, but thinks him a bit odd. Jamie only wishes he was half as brilliant but Samantha seems to like him just the way he is!

Their conversation is interrupted by a burst of activity around the Chameleon Tours kiosk. A tannoy voice announces the impending departure of Chameleon Tours' next flight - to Zurich. All passengers are encouraged to gather in the departure lounge. Jamie and Samantha are worried that something big is happening right under their noses, especially as there is no sign of Michelle/Polly.

The Doctor has raced to the Chameleon Tours hangar hoping to save Ben. There is no sign of him in the storage area nor in the office. A quick search does reveal the shiny pen-like freezing device obviously forgotten in a rush. The Doctor pockets it. There is no other sign of Ben's presence. Suddenly he remembers seeing the packing cases in the storage area and runs out to check them. Perhaps he's been stuffed in one of those.

Passengers have begun to assemble in the departure lounge for the next Chameleon flight. All of them are young people, most between 18 and 20. They all listen as a Chameleon Tours flight attendant, Ann Davidson, addresses them. She tells them that she wishes to save them some time on a tedious task - writing home when they get to Zurich. The crowd is pleased with this and eagerly grabs the stack of blank Swiss postcards she provides for them. They all begin writing generic "wish you were here" type messages on them. Ann promises to mail the postcards for them from Zurich. All of the kids, eager to get on with their holidays, agree to this and begin writing.

Samantha has infiltrated the group and heard all of this. She brazenly takes a postcard from one of the passengers and returns to Jamie's side. The cards already have unused Swiss stamps on them, ready for posting. All that is needed is the message to family. This would explain the card she got from Brian in Rome. The card was posted in Rome, but perhaps he himself didn't post it. Jamie finally understands and wants to go and tell the Doctor.

However, before they can move, they are stopped by a stern-looking man who would like a word with Jamie. It is Inspector Crossland.

In the hangar, the Doctor manages to prise open one of the cabinets just as Ben had done earlier. This one contains the body of George Meadows. The Doctor does not know the man but sees that he is wearing the uniform of an air traffic controller. He also notices the white arm band the man wears. He is still and ashen, deeply unconscious.

In the inner office, Spencer watches the Doctor on his monitor. He then activates a switch and a loudspeaker comes to life. A voice issues through the hangar, muffled and indistinct, but it is clearly begging for help. The Doctor thinks it could be Ben and tries to find the source of the voice. He goes back upstairs to the office. The voice abruptly stops. Suddenly a thick vapour hisses from a nozzle in the wall. It is a trap.

The Doctor turns toward the door but it is already closed and locked. He cannot get out of the room. The vapour becomes thicker, but it doesn't choke him. He approaches the nozzle trying to ascertain what is being sprayed from it and if he can combat it. It is not a gas but a freezing vapour. He snatches back his hand as the cold burns him. He is racked with shivers as the cold begins to affect him.

On his monitor, Spencer watches as the Doctor struggles back to his feet, showing remarkable resistance to the freezing gas. To his astonishment, the Doctor blocks the gas nozzle with a handkerchief. His strength seems to return almost immediately. But Spencer activates another control and another nozzle, higher up in the wall, appears spewing more gas.

The Doctor calls up his reserves of strength and slides a chair beneath the nozzle. He blocks the second nozzle and, for good measure, covers the camera with his coat while he's up there.

Spencer realises he must go out and find out what is happening. Emerging from the inner office, he sees the Doctor huddled on the floor in his shirt sleeves next to the overturned chair. Thinking the gas has finally done its work, he approaches the body. However, the Doctor is only feigning unconsciousness. He springs up, finding the silver pen device in his pocket and using it on a shocked Spencer. He freezes into immobility and slumps to the floor. The Doctor does not wait around to see what else will happen; he grabs his coat and races out the door, through the storage area and out of the hangar.

Back in the main concourse, Jamie has told his story to Inspector Crossland. Crossland is beginning to suspect that the murder victim was his colleague, Inspector Gascoigne, and while he is still concerned over Brian Briggs' disappearance, this takes priority.

The Doctor arrives out of breath and disheveled. Crossland is glad to see him and produces his warrant card. Jamie tells him that he's filled Crossland in on the whole story. The Inspector produces his photograph of Gascoigne and the Doctor can confirm that he's the man they found dead in the Chameleon Tours hangar.

Blade returns to the hangar to find Spencer just recovering from the effects of the freeze weapon. He is dismayed to see that the Doctor is not here; Spencer feebly explains that the Doctor's intelligence is far above "normal beings". Blade coolly announces that he must leave to pilot the Zurich flight but that Spencer will stay here and deal with the Doctor. To atone for his incompetence, Spencer must kill the Doctor.

Crossland has come to a decision - they must enlist the aid of the Commandant in dealing with this problem. There is clearly something larger than just one missing boy involved in this business with Chameleon Tours. The Doctor reluctantly agrees to go back there, hoping that Crossland's presence will lend credence to his story.

Samantha and Jamie are left once again to keep an eye on the kiosk, a task that seems a lot like doing nothing and Samantha is not thrilled. She decides to take matters into her own hands and investigate the Chameleon hangar. Jamie tries to stop her, explaining that the Doctor told them to stay put. She will not be dissuaded and casually laughs off the risk: what's the worse they can do? Kill her? Jamie rises to the bait and convinces himself it will be all right to leave the closed kiosk unwatched. He goes off with her.

The Commandant has been persuaded to listen to the Doctor and at last accepts - with Crossland's support - that he found a body in the Chameleon Tours hangar. Reluctantly, he listens to the rest of the story. The Doctor tells him of the body he found in the packing case in the hangar but makes certain they know he was not dead, merely in a comatose state. The Doctor does not know who he is, only that he is an air traffic controller, likely one who works in this very area. He looks around briefly, noting Meadows who tries to look nonchalant.

Next the Doctor produces the freezing device he stole from the office and shows it to Crossland and the Commandant. It may look like a fountain pen, but looks are deceiving. It is a very dangerous weapon. He decides to press his luck at this point, explaining that Inspector Gascoigne was killed by a ray gun not yet developed on Earth. The Commandant snorts with derision but Crossland is oddly supportive of the strange little man. Luckily for the Doctor he accepts this story so far and urges him to go on.

The Doctor says he believes that Chameleon Tours is merely a front for the mass kidnapping of young people, a suggestion that the Commandant cannot accept. Crossland, too, thinks it all unlikely even with the evidence of Brian Briggs' disappearance. With him gone as well as Ben and Polly, the Doctor is convinced of it. What's more, he is certain that the abductors are aliens. The Commandant is apoplectic at this and Crossland can barely calm him. Even the open-minded Inspector demands proof of this allegation.

The Doctor presents the pen device again, which is underwhelming to the Commandant and Crossland. The Doctor decides to demonstrate, grabbing a cup of hot tea from a passing tray and the nearest air traffic controller. It happens to be Meadows. The Doctor has him hold the cup out in front of him as he aims the device at it. Meadows reacts in fear, as if he knows what the device is and what it can do, but he stays put trying not to give himself away.

The Doctor fires the device and the man cries out and runs from the room, dropping the teacup. Jean picks up the cup which has remained intact despite the fall and shows it to all. The cup and the liquid inside are frozen solid. The Doctor is certain he has proved his point... and learned something very valuable.

Jamie and Samantha reach the Chameleon Tours hangar without incident and begin a search of the deserted storage area and office. Samantha finds an envelope full of postcards, perhaps the very same envelope that Inspector Gascoigne found. Reading them through she finds very generic greetings from the Black Forest, addressed to Mums and Dads, stamped and ready for posting. She shows them to Jamie, knowing she's found the proof that Inspector Crossland is looking for. They must hurry to show him.

However, Samantha's eyes begin to well up as she realises they may be very close to discovering what happened to her brother... and that it might not be pleasant. Jamie tries to comfort her but the strong-willed girl wipes the tears away and tells him she's just got something in her eye. She follows Jamie out of the hangar toward the Commandant's office.

In air traffic control, a change has taken place. Crossland and the Commandant examine the freezing device and are showing the Doctor a great deal more respect. Jean Rock provides the Doctor with a list of Chameleon Tours flight schedules as he has requested. Into the midst of this, Jamie and Samantha burst in looking for the Doctor to show him the postcards. He examines the envelope closely to find that it is addressed to Chameleon Tours in Germany. The cards are to be mailed there in a bundle and then posted back to their parents in England individually as if their children had arrived safely. His patience severely taxed by the strange assortment of characters invading his office, the Commandant nonetheless accepts the story. There is still the question of why these young people are being abducted and where they are being taken. The Doctor still has to work all that out. He studies the Chameleon flight schedules looking for a clue.

Meanwhile, the Commandant takes Crossland aside to get his take on all this, worried that this Doctor is unbalanced. However, Crossland realises that the Doctor has been highly effective in gathering information thus far and believes that he should be allowed to continue...with the Commandant's blessing. He takes responsibility for the Doctor upon himself and asks that he be given a free hand to investigate. For his part, the Commandant is simply to keep the airport running as normal so as not to alarm the Chameleon Tours people. Reluctantly, the Commandant agrees.

He gives the Doctor the freedom of the airport for 12 hours only. He must produce some real facts by that time or face the consequences. The Doctor thanks him for his (dubious) support. Samantha hugs Jamie, glad that something is at last being done to find her brother. He is none too pleased with this attention.

Meadows reports to Spencer at the office behind the Chameleon Tours kiosk, telling him what happened in air traffic control. Spencer is angry. Not only did Meadows make himself look suspicious, he left before learning whether the authorities believed the Doctor. The two men find it hard to believe that the Doctor has put all of the clues together so quickly, but they believe him to be unrepresentative of the beings on this planet. The authorities will not believe the Doctor because the truth is beyond their comprehension. On top of that, the Doctor will soon be eliminated.

Spencer produces a small button-sized device which will be used to kill the Doctor. Meadows is to find a way to attach it to him, then it will be activated by remote control and the Doctor will be dead before Captain Blade returns.

In air traffic control, the Doctor, Jamie, and Samantha receive their passes from Jean. The Doctor is drawn by an announcement that a Chameleon flight is entering radar range approaching Gatwick. He joins the controller at his station and watches.

The Doctor learns from Jean that Chameleon Tours makes 7 or 8 flights a day using 4 planes. It is fairly normal for a short-haul carrier like Chameleon which is only going to continental "hot spots" and returning. Short flights and quick returns.

Watching the blip on the radar screen, the Doctor wonders when the planes are first scanned on radar. The controller cannot answer that question. They don't even notice planes until they enter the air space and begin to call in. Similarly, they are not tracked after they leave Gatwick's control zone. The Doctor's mind is turning as the controller gives orders to Captain Blade to hold at 10,000 feet and await landing clearance.

Urged on by the Commandant, the Doctor decides to leave air traffic control and to continue his search in the airport. Jamie and Sam follow him. However, the Doctor bumps into a controller passing his way. The man grips the Doctor to steady himself and apologises. It is Meadows, returning boldly to air traffic control. He manages to slip the button-like device onto the back of the Doctor's coat. The Doctor thinks he recognises the man but Meadows says he's mistaken. Luckily, the Doctor is too preoccupied to pursue the matter and heads off.

Outside, the Chameleon plane lands, returning from its latest flight.

Inspector Crossland has also resumed his investigations, starting at the Chameleon Tours kiosk. Spencer is in charge there and becomes a bit nervous when Crossland produces his warrant card and insists on speaking to the person in charge. Spencer tries to put him off, explaining that Captain Blade is the man he wants but that he has just returned from one flight and is preparing to take off on another straight away.

Crossland will not take no for an answer, insisting on going out to the plane to speak with him.

In the back office, Spencer contacts Blade and tells him the trouble. Blade's response is cool and unconcerned: send the Inspector to the plane. He will deal with him.

The Doctor and Jamie have gone back to the Chameleon Tours hangar once again. Sam is not with them. They have gone straight to the office area. The Doctor noted during his struggle that the man who attacked him came from someplace within the office - a secret hidden area and he wishes to find it. They search all around, avoiding the walls where the gas nozzles are located. There must be a secret door.

Jamie joins in the search, his mind still occupied by worry about Ben and Polly. The Doctor assures him that all of this is connected and that finding the secret door will help them find a clue. They split up and start again, searching every inch of the little office. They must hurry. Crossland is keeping the Chameleon Tours staff busy for the moment, but the Doctor fears he may push too far and get into trouble.

Crossland has been escorted to the Chameleon plane, which sits on the tarmac already full of young people ready for a holiday. Ann Davidson is on board as flight attendant, collecting coats and seating the last passengers. Crossland speaks with Captain Blade, being blunt about his concerns. He explains about the missing boy and his missing colleague. Blade agrees that this is a serious matter and Crossland asks him to delay this flight so that he may make some inquiries.

Blade heads off to the flight deck to "make some arrangements" and Ann follows him. Crossland waits back in the passenger cabin until the sound of rising engine noises reaches his ears. Blade has lied to him and is going to take off anyway...with him on board! Crossland rushes to the flight deck and throws open the door. He is astonished at what he sees.

The flight deck is nothing like any aeroplane he has ever seen. There are banks of futuristic instruments and monitor screens, no steering controls, no pedals, nothing that would normally be used to fly a plane. What is worse, Captain Blade is pointing a weapon at him - one that looks suspiciously like a futuristic ray gun. Blade warns him to stay put; the strange weapon "proved remarkably effective" on Inspector Gascoigne. Crossland does as he is told and sits in a chair nearby. Metal straps emerge from the chair and hold him fast.

Blade says that killing Gascoigne was an unfortunate error as Earth people are more use alive. He notes that Crossland is a fine specimen and might be suitable "for the Director himself", but all this talk is lost on Crossland. He tries to warn them that "the long arm of British law" will see them punished for what they've done. Blade assures him cryptically that it will not reach where he's going.

Blade prepares the plane for departure.

The Doctor and Jamie are concentrating on a shelving unit in one wall and have removed almost everything on it. The Doctor discovers that one of the objects is actually fixed to its shelf and only moves sideways. When it does, the entire shelf slides back into the wall - the secret door.

In the secret office, the Doctor goes immediately to the small cabinet in the corner and opens it. He detects a whiff of some form of foreign gasses; it seems to be a support system for someone unused to the Earth's atmosphere. He then notes the monitors at the desk and activates their controls. First they see Spencer at the Chameleon Tours kiosk working innocently with a passenger, but a change of the controls shows a medical unit somewhere in the airport. A first aid post.

The Doctor thinks this an important clue and he and Jamie rush back to the main airport building to find the location of the medical unit.

Spencer finishes his work at the kiosk and returns to the office behind. He glances at the monitor and is astonished to se Jamie and the Doctor in the hangar office. He is furious and grabs the transmitter he showed Meadows earlier. He watches as they debate for a moment clearing up the mess they've made in the office. As they turn to leave, he activates the device.

In the hangar, the Doctor collapses to the floor, his body racked with pain. He calls out for Jamie to help him, indicating the pain is in his back. Jamie looks his friend over, trying to find the source of the problem. He finally spots the small black button-sized device and pulls it off, crying out in pain himself as he touches it. He manages to hurl it to the floor, but is he too late? The Doctor lies still on the floor, unconscious and unresponsive.

The Chameleon plane is now in flight and Ann moves through the passenger cabin. Each person takes something from the tray she is carrying. She seems the very model of a helpful flight attendant.

When she is finished, she returns to the flight deck, announcing that everything is all set. Blade switches on a monitor and makes sure that Crossland can see it clearly. It shows a view of the passenger cabin, lots of young people sitting side by side talking and laughing. He tells the Inspector that he is about to reveal to him the "secret" of Chameleon Tours.

The plane travels on, Crossland wondering what he has stumbled into.

Back in the Chameleon Tours hangar, Jamie tries desperately to wake the Doctor. Spencer arrives and announces that the Doctor is dead; Jamie is to come with him. When he refuses, Spencer produces a ray gun and orders him to leave the Doctor and come with him. Jamie is defiant - even more so when he spots Samantha arriving unseen behind Spencer.

Sizing up the situation quickly, Samantha decides a diversion is what is needed. She knocks over some drums behind Spencer and he instinctively turns toward the noise. Jamie then jumps on Spencer and tries to disarm him. Samantha joins in, jumping on Spencer's back. However, the two determined young people are no match for this alien in human disguise. He breaks free of them and retrieves his freezing device from his pocket. He makes short work of Jamie and Samantha. They freeze into immobility, slumping to the floor near the Doctor's body.

Spencer knows that his orders are to dispose of all the troublemakers but he was not told specifically how. He decides on a novel form of death. After freezing the Doctor (for good measure), he sets up a laser-beam system attached to a nearby wall and activates it. The beam projects downward to the floor and begins traveling slowly across to where the helpless Doctor and his friends lay unaware. Spencer then leaves the hangar, certain he has done his job.

Inspector Crossland has regained his senses somewhat. His own life seems safe for the moment, so he tries to extract some information from his captors. Blade however will not reveal where the plane is headed, although it's certainly not Zurich. Blade activates the communications system and makes a worrisome announcement. He would like to inform "the Director" that he has "an original" for him. The "original" is Crossland himself.

Samantha and Jamie are quick to regain consciousness to find themselves on the hangar floor. However, both are still immobile from the freezing ray. The Doctor eventually comes to as well. He is first to notice the beam of light moving toward them. Neither Jamie nor Samantha realise what it means until the beam ignites a pile of debris on the floor nearby. The Doctor tells them that it is a small foretaste of what is to happen to them once the beam reaches them.

All of them struggle to try and move. They cannot get up nor can they move out of the way. Samantha has managed to get one arm moving, but just barely. Things look bad.

In the medical unit, another transformation is taking place. Nurse Pinto supervises the operation as another of the faceless, misshapen alien creatures takes on the likeness of a human being. This time, the victim is Immigration Officer Jenkins.

In the hangar, the Doctor has come up with a long-shot plan to defeat the laser beam trap. Samantha has managed to reach her handbag and the Doctor is hoping that she has a mirror in it. Fortunately, she does, and uses her free arm to produce it. The Doctor is sure it will work for the plan he has in mind, however, passing the mirror to him proves impossible due to their paralysis.

Jamie, closer to Samantha than the Doctor is, can just get hold of the mirror but cannot move his arm enough to pass it on. He will just have to carry out the Doctor's plan on his own. The plan is to catch and reflect the light beam back using the mirror in an attempt to destroy the projector and save them all. After a quick instruction from the Doctor, Jamie pushes the mirror into the path of the light beam, which is now very close to them all. The problem is keeping his hand from being burnt, but Jamie will just have to take that risk.

All three hold their breath as the beam approaches. There will be only one chance. At a shouted order from the Doctor, Jamie pushes the mirror into the beam. It is at the proper angle and the beam reflects back, destroying the laser projector in a puff of smoke. The beam disappears and they are safe. They can all breathe again.

Before long, they can all move again as well. Luckily, the effect of the freeze ray is fairly brief. Jamie's mind has already moved ahead of their own predicament and he fears that this laser death trap might have been tried on Ben and Polly. The Doctor is certain that is not the case. He believes that they were needed alive for some other purpose. Clearly the three of them were deemed too dangerous to keep alive and that means one thing to him: Chameleon Tours' plans are very advanced and they must act fast if they are to stop them and save Ben, Polly, and Samantha's brother.

The Doctor decides that their next move should be to investigate the first aid post they saw on the Chameleon monitor. It appeared to be a centre of activity and one which has not yet been investigated. However, the Doctor is concerned about them all going together. It will be too suspicious. The Doctor decides to send Samantha back to the Chameleon Tours' kiosk in the airport to keep an eye out for the man that tried to kill them. She must be careful that he doesn't see her alive and well, but the Doctor seems to hope he'll be careless now that he thinks he has disposed of them. Samantha hurries off.

Jamie is proud of how courageous she is, but the Doctor worries that she might prove to be too adventurous for her own good.

In the medical unit, the new Jenkins is undergoing his final physical and mental tests. The human "original" is out of sight for the moment and the new Jenkins wears his black arm band prominently. He performs just as well on his tests as the new Meadows did. Nurse Pinto is pleased.

However, the tests are interrupted when the Doctor and Jamie burst in to the medical unit. The Doctor is supporting the lad, who grimaces in pain and breathes very heavily. Satisfied that this is the place he saw on the monitor, the Doctor plunks Jamie into a chair and warns him against overacting before turning his attention to Nurse Pinto.

Pinto hastily ushers Jenkins out of the unit, pretending to be sending him off with some medicine, then turns to the Doctor. The Doctor says that Jamie suffers from a "rare tropical disease" and that his condition is dire. If he doesn't recover soon, he will have to give the lad "somnalin", a drug which the nurse has never heard of - likely because it doesn't exist.

What the Doctor really wants is somewhere to lay Jamie down to rest. This is an excuse for the Doctor nose quickly around, looking for the right sort of place. He goes into the inner room and finds a cot but it is in the "x-ray" area where the alien/human conversions are made. Luckily, Nurse Pinto had hidden Jenkins' original away before the Doctor arrived. She is forced to stumble around for a moment before she finally tells the Doctor that Jamie cannot lie down in there as she has a patient coming in for an x-ray soon. It sounds lame when she says it but the Doctor cannot contradict her. He only asks innocently why she didn't mention that at first, then begins gathering up his "patient" to leave.

In the small office behind the Chameleon Tours kiosk, the new Jenkins has hurried to report the intrusion into the medical unit. He and Spencer watch on the monitor as the Doctor and Jamie leave. Spencer is more angry than ever at the Doctor's interference. Jenkins joins him, determined to succeed in killing the Doctor. Spencer has another idea - let the Doctor and his friend come to them....

In air traffic control, Jean and the Commandant are trying to find out what has happened to Inspector Crossland, whom they have been trying to contact with no luck. The Doctor arrives and finds this out. He is quite concerned. There is also a message here for the Doctor from Samantha Briggs. The Doctor decides to send Jamie to her to make sure she's all right.

The Doctor learns from the Commandant that Crossland was going to investigate Chameleon Tours and is certain that he has now disappeared. The same thing happened to Ben and Polly and it is not a far leap for him to suspect a similar fate for Crossland. However, the Commandant recalls the Doctor's other "leap" in suspecting aliens and is sceptical.

Jean finishes a phone call and announces that she has new information regarding Chameleon Tours. Slightly stunned, she reports that she has made inquiries at all the airports to which Chameleon Tours flies. Dubrovnik, Athens, Rome, all of them. The response was the same - Chameleon Tours never deliver passengers! They land and pick up young people at all of these places, bound for one of the others. No airport reports any passengers ever disembarking from a Chameleon plane.

The Commandant is stunned as well at this news, but refuses to believe the Doctor's theory about aliens. However, he does plan to take action. Captain Blade's flight is due to return in half an hour, with another flight scheduled immediately after. The next time that plane takes off, it will be followed. The Commandant gets on the phone to the nearest RAF station.

Meanwhile, the Doctor is already several steps ahead. He takes Jean aside to discuss a plan with her. He explains that he thinks the medical centre in the airport is connected with this abduction business and that he wishes to investigate it without Nurse Pinto around. He is hoping that Jean will help him distract her...

Jamie reaches the Chameleon Tours kiosk and finds Samantha neck-deep in trouble. She has purchased a ticket for the next Chameleon flight - to Rome. That is where her brother disappeared and she is certain that she will learn something valuable if she follows in his footsteps. Despite the obvious danger, it is all she can think of to remain pro-active in this investigation. Jamie chastises her for the precipitous action but cannot stop her.

He suggests that he go along, but does not have the money to purchase a ticket. To him, £28 is a fortune. But he is determined to stop her from doing something so dangerous. When she turns away from him for a moment, Jamie spots the ticket sticking out of her bag and decides to steal it. She nearly catches him and he is forced to give her a sudden hug and peck on the cheek to distract her. While Samantha hugs him, he swipes the ticket.

In air traffic control, the Commandant has called in a favour and arranged for an RAF fighter to tail the next Chameleon Tours flight, heading to Rome in less than half an hour. He is satisfied that he will find the "secret airfield" to which they are transporting these young people and that it will have nothing to do with aliens or ray guns. Suddenly and without warning, Jean Rock crumples to the floor, unconscious. The Commandant is stunned and calls immediately for the medical centre.

Nurse Pinto takes the call. She tries to get out of leaving the medical unit but the Commandant will not take no for an answer. She slams the phone down angrily and grabs a medical bag before leaving. She is loathe to leave the place unattended but she cannot do so without breaking her cover. She heads out.

As soon as she is gone, the Doctor sneaks in. He knows he has little time and goes immediately to the inner room where the "x-ray" machine stands. He examines the machine for a moment, noting quickly its unearthly design and guessing as to its function. He then goes to examine a cupboard in the corner. It is locked, but he quickly picks the lock and opens it. It is full of the black and white arm bands used on the "originals" and "copies". He takes one of each and puts them into his pockets.

Little does the Doctor know that his intrusion here has been expected. In fact, Jenkins has followed him in and now waits in hiding with his ray gun drawn. The Doctor completes his search and starts to head quietly out, not seeing Jenkins at all. Jenkins starts to come out of hiding, ready to shoot the Doctor in the back, but is stopped when another man enters the medical unit. He is simply a traveller looking for some medical help.

The Doctor becomes aware of the man behind him and knows that he has just been saved from an untimely demise. Glibly, the Doctor tells the passenger that he himself is "just going off duty" but that Jenkins will be glad to see to him. Then he is gone, certain that Jenkins won't be able to follow him. Another narrow escape.

The Doctor returns to air traffic control as Nurse Pinto continues her examination of the now-conscious Jean, unable to find any reason why she fainted. Seeing the Doctor, Jean suddenly stands up, completely fine. The nurse seems unaware of the oddness of this and continues asking questions. When Jean says she hasn't eaten all day, Nurse Pinto assumes this is the cause and chastises the Commandant for working her too hard. She is playing the part of a medical professional to the hilt, storming out under a cloud of righteous anger.

The Commandant cannot understand what has happened, but realises the ruse when the Doctor congratulates Jean on a job well done. The Doctor admits he convinced Jean to fake the illness and produces the two arm bands. The angry Commandant wants an explanation and the Doctor goes to find the fake Meadows to provide it. But he is not here and another controller sits at his radar station. Meadows must be off duty for the moment and should return in a few hours. The Doctor is saddened, certain he had found definitive proof of the presence of aliens here, but that will just have to wait now.

In the airport, a boarding announcement is called for Chameleon Tours' flight to Rome. The passengers hand their pre-written postcards in to stewardess Ann Davidson. All except for Samantha, who has mislaid her ticket and cannot find it anywhere in her handbag. Samantha is getting more cross by the moment. She appeals to Ann to remember her purchasing the ticket, but the stewardess does not. Samantha gives her name, noting that the ticket simply said "S. Briggs" on it, and Ann does some checking.

In the office, Spencer watches this exchange on his monitor. Ann reports that "S. Briggs" has already checked in and boarded the flight. It was not a woman but a young man. Samantha realises that it has to be Jamie who stole her ticket, just to keep her off the flight. She is very angry and demands that the flight be stopped and Jamie be found. Ann refuses to do so.

Spencer phones up to the front with a message for Ann. She tells Samantha that her ticket has been found and that she can go on the flight. However, the "manager" would like to see her first. Ann points her to the office behind the kiosk and returns to collecting postcards from the other young people clamouring for that trip to Rome.

Samantha steps into the office and is stunned to see Spencer there - the man who tried to kill them all with the laser device in the hangar. He is armed with a ray gun and a freeze weapon. He assures her that she will not escape again.

Shortly, the Chameleon plane is requesting clearance for takeoff, which is granted by air traffic control. The Doctor and the Commandant look over the shoulder of the controller guiding the flight. The Commandant is confident the fighter will solve their problem, but the Doctor thinks not. He believes the fighter will not be able to fly high enough to find out where the Chameleon aircraft goes.

After takeoff, the Commandant calls to RAF Station Manston and gives the word for the pursuit plane to get in the air, passing on precise heading information.

On board the Chameleon plane, Ann is checking over the passengers. She notices one young lad looking quite green and rather scared. It is Jamie. He has never flown before and the sensation is not pleasant. Jamie laughs it off, assuring her he's fine, but when she presents him with some refreshment, he turns greener still and leaves his seat for the toilet... in a hurry!

The Chameleon plane reads as an anonymous blip on the radar screen now, 59 miles out from the airport. The Commandant tells the Doctor that they normally do not track the planes this far by radar as there's too much air traffic to contend with. They are on their own out that far. A radio call comes in from the RAF fighter pilot - he has the Chameleon aeroplane in sight and is following at a distance. The radar confirms it as his plane appears in the same course as the Chameleon plane. The Commandant is still confident at this point.

Ann returns to the flight deck and announces - as before - that all is in readiness. Blade activates the controls and on the monitor they can both see that the entire planeload of passengers has disappeared. Ann picks up a large segmented tray and starts to return to the passenger cabin to repeat the usual routine on every flight. However, Captain Blade stops her. He has detected something following them.

Ann joins him at the scanner. Blade realises quickly that it is a fighter plane, small and fast and right on their track. He acts quickly, activating several controls whilst Ann gets a precise fix on the plane. Once that is done, Blade presses a button.

Suddenly the fighter is engulfed in a burst of energy and the pilot cries out. He then slumps forward unconscious. His controls go dead and the plane starts to fall like a stone into the sea.

The Commandant is first to notice the problem. The fighter's has veered suddenly away from that of the Chameleon plane and the controller tries to raise the pilot by radio. There is no response and with sinking hearts they all begin to fear the worst. The Doctor is sad and silent but the Commandant refuses to give up. The plane drops out of radar range and he issues a call to RAF Manston to report it.

But there is more. The controller notes that the Chameleon plane's blip has stopped moving forward as well. It is standing still on the screen, a physical impossibility. The Commandant knows that its sudden disappearance from the radar screen can only mean one thing - the Chameleon plane is crashing too.

But that is not the case. In fact, the Chameleon plane is still moving, only upward and not forward. Its nose is now pointing skyward and its wings fold back into a sleeker, more unearthly shape. No longer does it get its power from jet engines, but from rocket engines. The aeroplane has turned into a spaceship, heading straight up into the heavens.

On board, Ann is in the midst of her task in the passenger cabin. She seems to be picking up something from each seat and placing it into the segmented compartments of her tray. Blade calls her back to the flight deck and she stops what she is doing.

Blade asks her how many people require passports in order to leave the airport on the next flight and she says 25. However, she has missed one and he corrects her sternly. Things must be precise in order that their plans remain undetected. She hurriedly returns to the passenger cabin to resume her collecting. However, the seat where she wishes to start is empty. She finds this strange but assumes that she has already picked that one up and simply forgotten in the confusion. She moves on. This was the seat that Jamie had occupied.

Jean receives a report from the rescue team sent to investigate the crash of two planes. They have found nothing. No debris, no survivors, nothing. The Commandant cannot understand it, but the Doctor believes he has the answer. The fighter veered off course before disappearing from the radar, presumably diving downward as it went. However, the Chameleon plane stood completely still before it disappeared from the radar. The Doctor is certain it did not go down but up. Straight up from a dead stop.

The Commandant thinks this is nonsense as no plane can do that. It would have to be a spaceship to go straight up out of radar range. The Doctor wholeheartedly agrees.

The Chameleon rocket ship lands on the space station. Ann and Captain Blade start to disembark, Ann carrying her compartmentalised tray. She is concerned over the destruction of the fighter plane, worried that it might make the airport authorities suspicious. But Blade cares little about this, his perceived superiority over the humans unshakeable. He reminds Ann of the teaching of their Director: human intelligence is comparable to that of the animals on their planet. With that, they leave the plane.

Jamie has been hiding in the lavatory since bolting from his seat. He has avoided the fate of all the other passengers and does not know what has happened to them. As Ann and Blade leave the plane, he sneaks out determined to follow them.

They lead him into a featureless corridor that seems endless. He stays far enough behind so he will not be noticed. Ann turns a corner and he follows. When he turns, neither she nor Blade are anywhere around. However, there is a door in one wall that stands open. He moves quietly to it, peering in.

Blade is still nowhere around, but Ann is there. She is transferring the contents of her tray into other compartments in what look like file drawers. When she is finished, Jamie ducks back out of sight. Ann leaves the room and carries on down the corridor. Jamie worries about what to do next, but his decision is made for him when he hears voices approaching from down the corridor. He ducks into the room and closes the door.

Once in the room, he cannot help but start to look around. He goes first to the drawer in which Ann was working just moments ago. There are many such drawers all over the room. Opening the drawer, he finds many segmented compartments, each filled with a tiny doll. They are small replicas of human beings. But upon closer inspection he recognises the features of his fellow passengers on the plane he has just left. To his horror, he realises that these are not dolls at all, but miniaturised people!

Every drawer in the room is filled with people, kidnapped from Earth and shrunk to doll size. It occurs to him that Ben and Polly, as well as Brian Briggs, are likely here in one of the drawers. He himself has only barely escaped the same fate.

Jamie is startled by a voice at the door. It is Ann Davidson, returned to find him standing over the drawer. She was almost certain she had missed a passenger on the last flight when Blade interrupted her. Now she knows that he escaped. Jamie is horrified and demands an explanation for what he has seen. Ann is in no mood for conversation. She is armed with a ray gun but does not use it. Instead, she steps aside to allow two of her faceless, misshapen comrades into the room. She then backs away, closing a frightened Jamie in with the hideous creatures.

Back on Earth, in air traffic control, the Commandant receives the sad news that the wreckage of the RAF fighter has been found. The pilot had been electrocuted prior to the crash. To the Doctor's mind, this proves his point. They are not dealing with human beings. The Commandant is still hard-pressed to believe it, despite the preponderance of evidence. He still wants more proof from the Doctor. Looking toward the doorway, the Doctor believes the proof he's looking for has just walked in. Meadows.

The alien masquerading as George Meadows comes on shift and takes his usual place at the radar screen. The Doctor asks for permission to question him but does so before the Commandant can answer. He presents the man with the black and white arm bands he found in the medical centre and asks if he recognises them. Meadows pleads ignorance, a bit calmer than he was when faced with the freezing weapon earlier.

The Doctor persists, asking Meadows to roll up his sleeve. The Commandant is not sure he should allow this treatment of his employees, but the Doctor tells him firmly that this is not one of his employees. The Doctor says that airport personnel are being systematically replaced and the arm bands are involved. This is not Meadows and he is wearing an arm band. Reluctantly, the Commandant agrees and orders Meadows to comply.

Meadows starts to roll up his sleeve, his calm demeanour starting to crumble. Suddenly he bolts from his chair and makes a run for the door. The Doctor calls out to stop him and Jean obliges, blocking his path and causing him to crash to the floor. Two men grab him and haul him back to a chair at the Doctor's orders. Meadows sits passively by as one of the men rolls up the sleeve of his jacket. As expected, he wears one of the black arm bands.

The Doctor presses on, preparing to adjust one of the controls on the band. Meadows abandons his passivity and begs him not to touch it. The Doctor now knows he has control over the man and begins questioning him - if he answers the questions, no harm will come to him.

The alien disguised as Meadows reveals that there was a gigantic explosion on their planet and his people lost their identities. Hence their blobby, misshapen, unfinished appearance. They are also dying out. Their scientists have devised a way for them to take on the physical characteristics of other beings which is their only hope for survival. The arm bands are a vital part of the process. The aliens are abducting the young humans in order to assume their physical form and thus survive. They are planning to abduct 50,000 young people in this go. Each planeload is miniaturised and taken to a satellite in orbit 150 miles above the Earth where they are stored. The Doctor takes all this in calmly and rationally. It all makes sense to him now.

The Doctor wants to know how many of the aliens are working here at Gatwick but Meadows does not know. Even under the threat of removal of his arm band, he insists he does not know. He does however reveal that the "original" humans are being held somewhere in the airport. He doesn't know where but begs that they not be found. He clams up at this point, but the Doctor realises why. If the humans are found and the arm bands removed, something terrible will happen to the aliens masquerading as them. The aliens can be changed back to their normal faceless selves, but only with the aid of the machine. Any tampering with the arm bands unaided will bring about disaster.

Meadows again insists that he doesn't know where the original humans are kept, except for the original of Nurse Pinto. He says that the alien who took her identity kept the original with her. It is in the medical centre. The Doctor must threaten to disturb the controls on the arm band but eventually Meadows agrees to show him where Nurse Pinto's original is. But he is defiant to the last, vowing that no matter what the Doctor does, he will never see those 50,000 young people again!

The captive Samantha has not been put aboard the Chameleon plane but has instead been taken to the medical unit. She is gagged and bound to a table. Nurse Pinto checks her over, at a loss as to what to do with her. She contacts Spencer, who tells her that Samantha will be used as an original for one of their people. Once they have taken her identity, they can get close enough to the Doctor to destroy him.

Before Nurse Pinto can ask any further questions, she is interrupted by an intrusion to the medical unit. She quickly cuts off the communications device and turns to see the Doctor. Admirably, she maintains her calm, even when Meadows is brought in by two policemen. She continues to play the part of a nurse but the Doctor cuts through her façade. He has one of the policemen hold her and roll up her sleeve to reveal the black arm band she wears. As he suspected, she is an alien in disguise.

The Doctor makes certain to remove the freezing device Nurse Pinto wears clipped to her uniform before heading for the back room. It is there, Meadows says, that the original Nurse Pinto is hidden. The alien Pinto tries to stop him but one threat against her arm band silences her. Once policeman and Meadows follow him in.

Samantha is very glad to see the Doctor and to have her gag removed. However, he rolls up her sleeve - checking for a tell-tale arm band - before freeing her. Then he has Meadows find and activate the controls to reveal the hiding place for the real Nurse Pinto. A wall panel slides away, showing the real Pinto in a stupefied state and wearing a white arm band. She is alive but unmoving. Samantha is stunned, to say the least.

In the outer room, the alien nurse waits while the policeman watches after her. But he has not been prepared for what he is facing and does not recognise the alien ray gun sitting nearby as a weapon. Pinto waits for a moment of distraction and makes a very quick dodge for the gun. She points and fires in nearly the same motion. The policeman is killed instantly.

Pinto enters the back room where everyone's attention is on the figure in the hidden cupboard. Pinto raises her gun to kill Meadows for betraying their people and their plans. But Samantha sees her first and shouts a warning which galvanises them all. Thinking quickly, Meadows reaches in and adjusts the controls off the band on the real Pinto's arm.

Suddenly the alien replica of Nurse Pinto disappears, reduced to a quivering blob on the floor. Her black arm band is all that is left recognisable. It is a horrible sight for them all. Clearly, this result is what Meadows feared from the Doctor - the reason why he cooperated.

The real Nurse Pinto - now the only Nurse Pinto - comes out of her frozen state and slumps forward. Meadows and the Doctor help her onto the table most recently occupied by Samantha. The Doctor examines her and Meadows assures him she has suffered no permanent damage. The arm band comes off and Nurse Pinto opens her eyes. The Doctor tries his best to reassure her that she will be fine in a few minutes.

His attention is drawn to a stack of files on a table nearby and he beings looking through them with great interest. So much interest that he doesn't listen at first to Samantha, who is trying to tell him about Jamie. She had assumes that the Doctor himself had gotten Jamie to steal her ticket, but that is clearly not so. Soon the Doctor realises what she is saying: Jamie's gone on a Chameleon flight, the one he watched disappear from radar! Very worried for his friend's safety, the Doctor grabs the files and races from the room. On the space station, Jamie has been tied up and left alone in the storage room. He cannot get free. Suddenly someone enters, perhaps the last person Jamie expected to see. Inspector Crossland. Jamie is thrilled all the same, especially when he begins to untie him.

Jamie explains how he got here by stealing a ticket for the Rome flight but Crossland is surprised that he's here at all. He should have been miniaturised on the flight like all the other passengers. Jamie explains that he got ill and didn't eat or drink anything. Crossland tells him that the food is actually part of the miniaturisation process which explains why he was unaffected. Crossland also tells him where they are and that the Doctor was right about the abductions being perpetrated by aliens.

Jamie is stunned but believes him. He has always trusted the Doctor's theories, no matter how wild they may seem to him. Crossland wonders if the Doctor has convinced anyone else back on Earth and Jamie thinks perhaps the Commandant has started to believe but really doesn't want to discuss it any more. He is ready to break out of here and escape back to Earth on the next flight.

Strangely, Crossland tells him that will not be possible. The last flight to Earth is getting ready to leave now. The aliens have completed their abductions and are only returning to pick up the last of their own people. His words sound very final and defeatist but Jamie is certain the Doctor will think of some way to stop them and rescue his friends. Crossland tells him that will not be possible. The Doctor is outmatched by the aliens and especially by their leader, the Director. He is far more intelligent that the Doctor.

Jamie cannot understand this shift in the Inspector's demeanour, nor can he figure out how he knows so much of the aliens' plans. Jamie soon receives the chilling answer: this is not Inspector Crossland at all, but the Director himself. He has taken over Crossland's identity. Jamie is stunned.

Meanwhile, the Chameleon space ship leaves the station and heads back to Earth for its final pickup.

In air traffic control, the Commandant keeps his controllers sharp on their radars. The Chameleon flight is due to and at any time and he wants to know the moment the plane appears on radar.

The Doctor has returned, bearing the files he took from the medical unit. They are the personnel files of 25 airport employees, all of whom are now being impersonated by the aliens. The Doctor calls the aliens Chameleons. The Commandant is ready to have them all arrested but the Doctor thinks that unwise, especially when he realises that the next Chameleon Tours departure is the last scheduled for the season. He knows that their plans are very advanced and the entire operation could soon shut down. If they've any chance of rescuing the 50,000 abducted young people, the Doctor must get aboard that flight and reach the Chameleon space station. The only way he can do that is if Chameleon Tours is allowed to operate normally and they do not get wind that their plan is now known. The Commandant reluctantly agrees.

They are interrupted by an announcement that an unidentified blip has appeared on radar. It is very likely the Chameleon plane returning.

The Doctor learns from Meadows that it is possible for the aliens to be "processed" more than once - meaning that the alien who looks like Meadows could theoretically be stripped of that identity and given a new one. It is not unusual. The Doctor hopes to use this fact to get himself on the Chameleon plane. He will pretend to be Meadows, reprocessed to adopt the Doctor's identity. Once up on the satellite, he hopes to try and bargain with the Chameleons for the return of the young people, but his bargaining power depends upon the Commandant. Somewhere in the airport are the 25 human "originals" that were taken over by the Chameleons, just as Nurse Pinto's original was. The Commandant must find those originals and hold them - doing nothing to affect the arm bands they wear - so that the Doctor can have something with which to bargain. The Commandant agrees to turn the place inside out, knowing what he must do even though the situation is almost too fantastic to contemplate.

The Doctor now prepares his plan for getting onto the Chameleon plane, and for that he will need the help of the real Nurse Pinto.

Some time later, the Doctor is on the table in the medical unit and Nurse Pinto pretends to be completing his transformation from alien to Doctor. The Chameleon plane has returned to Gatwick Airport and Captain Blade has made straight for the medical unit. He enters to find the Doctor and immediately pulls out his ray gun. Nurse Pinto tells him the situation and he hesitates. The Doctor, putting on a calm Chameleon demeanour, says that Meadows got to be too suspicious an identity but that he was able to kidnap the Doctor and change identities. Blade appears to accept this and puts his gun away.

Blade is sorry to have to lose their operative in air traffic control, but glad to have the meddling Doctor out of the way. Blade is ready to bring them all on the final flight, even though the Doctor seems to have forgotten all the pertinent details. He convinces Blade that the processing has scrambled his brain a bit and takes the passport provided to him. With Jenkins working for them in Immigration, they will have no problem getting out of the airport and onto the flight. Blade inquires as to the location of the Doctor's "original" and the Doctor says only that it is safe. Blade almost reveals the locations of the other originals but decides against it. It would waste too much time to move the Doctor there. He informs the Doctor and Pinto that they plane leaves in 15 minutes and then leaves the medical unit.

The Doctor can only hope that they've managed to convince Blade of their story as they hurry off for the aeroplane.

Jean receives word in air traffic control of the passengers embarking on the Chameleon flight. They are all adults; all airport personnel. The Doctor and Nurse Pinto were among them. The Commandant is relieved but knows that time is now very short for him to find those originals. He gives the Chameleon flight clearance to take off.

Blade wastes no time in taking off, heading out toward a fictional destination.

The Commandant watches the plane on the radar screen. As before, it goes out a certain distance and then stands still in the air. It is soon off the screen, rising above the radar umbrella. The Commandant places another call to Superintendent Reynolds, urging him to commit every available man to the search for the missing originals. Time is rapidly running out.

Jean and Samantha have joined the search as well. Samantha has searched the Chameleon kiosk and found very little. She has a small sheaf of papers but there seems to be nothing of interest on them. She has joined Jean in the medical centre. She is having even less luck. They give up the search and return to air traffic control.

They present their meagre findings to the Commandant, who is becoming more desperate by the minute. He takes the papers from Samantha and starts to study them. He is very well aware that the lives of thousands of young people are riding on them.

Aboard the Chameleon plane, the Doctor and Nurse Pinto try their best to avoid the other Chameleons as they travel from the atmosphere and into space. Pinto seems to be holding up bravely in the face of all the strangeness, but the Doctor can tell that she is nervous. He reassures her that all will be well. They should soon arrive.

He is right and shortly the spaceship has landed on the satellite. The Chameleons start to get up but they are stopped when Captain Blade arrives in the passenger cabin. He announces that due to the success of their operation, living space on the satellite has had to be reallocated to contain their "cargo". All of the people on the plane are directed to the accommodation centre for new instructions. He moves off, followed by the others.

Nurse Pinto and the Doctor hang back a bit, worried about this announcement. They both fear that it could be a ruse to forced them to reveal themselves. The Doctor is determined not to let that happen. They hurry off to follow the others.

Elsewhere in the station, a conversion operation is being completed under the supervision of the Director himself, still in the guise of Inspector Crossland. The new duplicate is Jamie! The alien with Jamie's identity sits up from the table and undergoes the usual testing. Some work must be done to perfect his voice control, but there is a slight problem - "Jamie" speaks without his Scottish accent. Other than that he is a perfect replica.

Captain Blade enters with news, two impostors have infiltrated the satellite - the Doctor and Nurse Pinto. He knew all along and now he wants permission to kill them both. However, the Director holds back. He asks the false Jamie for information on the Doctor and learns that the strange little man is a traveller in time and space. Accessing Jamie's memories, the Chameleon reports that the Doctor's knowledge is greater than their own.

Given this, Blade is sure the Director will order the Doctor's death. Surprisingly, he does not. His mind must be harnessed to work for the Chameleons. Blade is stunned and angered at this lack of foresight and protests. The Director silences him with one order.

The Doctor and Nurse Pinto still follow the group of Chameleons down a corridor. They have been walking for some time and are seemingly going nowhere. However, Captain Blade is nowhere about and the Doctor is emboldened. He decides to slip away from the group and try to search the station for the missing young people.

Unfortunately, they do not get far at all before they are confronted by Captain Blade. The Doctor tries to bluff, saying he and Pinto are looking for the accommodation centre, but Blade's pretense is gone. It is very clear that he knows the two are impostors. He tells them ominously that they no longer require living space.

The hideous, misshapen, faceless alien forms of the Chameleons...

The Doctor tries to bluff Captain Blade, pretending to be a Chameleon. But Blade knows he is lying and lets him know that. However, the bluff will soon become true. He and Nurse Pinto will be taken over by Chameleons very soon.

Back on Earth, the search for the missing originals continues. Police Superintendent Reynolds has come to air traffic control to update the Commandant on the progress and to question Meadows. Both men are convinced at last that Meadows does not know where the originals are hidden.

Reynolds indicates on an airport map the areas already searched. Police are going over several areas now but there is still a large portion of the airport uncovered. Time is running short and they need more help. Taking charge as is his custom, the Commandant boldly cancels all inbound and outbound flights and makes an appeal over the PA system for all airport personnel to join the police and assist in the search.

Out on the airport grounds - in all the hangars and offices and storage areas - the search intensifies.

The Doctor and Nurse Pinto are taken to the Director's office. The Doctor is a bit surprised to see that the Director has taken on the form of Inspector Crossland, but at least that means the real Inspector is safe somewhere here on the station. The Doctor tells the Director that he is here to plead for the release of the abducted young people. It is clear the Doctor knows the whole situation. The Director is unmoved, showing his contempt for these mere primitive humans. He reminds the Doctor that the Chameleons are the most intelligent race in the Universe.

A technician in human guise announces that the Freiburg flight has just taken off, bearing the Chameleons from the German office. Only Dubrovnik and Athens remain before the operation is complete. The Doctor recognises Jamie even without his Scottish accent and is again saddened to discover his friend's identity has been appropriated. However, when the Director tells him that Jamie's original is somewhere in the station, the Doctor has an idea.

The Director wishes to get on with the processing of the Doctor and Nurse Pinto; he will happily choose which of their people will get to inhabit the Doctor's persona and have access to his brain. With this, the Doctor enacts his plan, playing up the fact that some favoured Chameleons get to have their originals with them here on the station. The others - like Blade and Spencer - must trust that their originals will remain safe in hiding back on Earth. He remembers well Meadows' take on the subject and bets that others feel the same way. The Director realises what the Doctor is up to and silences him. The originals at Gatwick Airport will never be found.

Unnoticed, Blade and Spencer seem a bit dubious of this assessment.

Back at the airport, the Director's words are proving hard to dismiss, however. The ever-widening search has still turned up nothing.

A short time later, Blade, Spencer, and Jamie are left to process the Doctor and Nurse Pinto. The Director is gone for the moment. The Doctor seems to have struck a nerve with Blade, who asks for clarification of what he was saying earlier. The Doctor draws a sharp line between the fortunate Chameleons - like Jamie and the Director - whose originals are safely aboard the satellite, and the less-fortunate whose originals have been left on Earth at the mercy of anyone who might find them and tamper with the vital arm bands.

Blade thinks about this for a moment but decides that the Doctor is bluffing. The processing must commence. The Doctor continues to up the ante, saying that the Commandant has found the originals and has orders to deprocess them one by one, starting with Captain Blade, unless the Doctor radios him and stops him. He is forced to deflect the question of where the originals were found but insists he is telling the truth. It is a desperate gamble, but it is all he's got. He urges Blade to contact the Commandant by radio to confirm his story.

After a long moment, a nervous Blade decides to do this, ordering Jamie to establish communications with Gatwick control.

At air traffic control, Reynolds updates the Commandant on search progress via the map. Controller Heslington interrupts with news that a strange message is coming through the communications. They are asking for the Commandant. He steels himself and responds.

The voice is that of the false Jamie, inquiring in a strangely vague way about "some property" which the Commandant may have found. The Commandant is quick to catch on, stating definitively that they have found "the property". He must obfuscate about the location of the originals - as the Doctor did - but he assures the Chameleons that he can destroy them now. Jamie puts them on stand-by while the information is considered. The Commandant and Superintendent Reynolds can only hope that they have helped the Doctor with whatever bluff he is attempting.

Meanwhile, Samantha has led Jean back to the little office behind the Chameleon Tours kiosk. She has remembered something she had earlier dismissed in her first search of the office. A short search yields a forgotten piece of paper, on which is listed only car numbers, nothing else. But there are 25 of them.

Samantha had originally dismissed them as merely a list of coaches owned by Chameleon Tours, but once she realised they had no need for coaches, it all became clear. 25 numbers, 25 originals. They are hidden in cars somewhere in the airport's giant carpark.

Jamie returns to the radio and wants to know why the Commandant won't state where the originals were found. He and Reynolds must bluff again, saying they were found by the police who have not divulged their location as yet. Jamie goes on hold again to consider this. Reynolds and the Commandant are sweating bullets.

A telephone call rings through and Reynolds takes it. It is Jean and Samantha with the information about the car numbers. The Commandant, buoyed by this information, turns to the communications unit to try and stall the Chameleons until the lead can be followed down. But he is too late. The Chameleons have not believed him and have shut down communications.

The Commandant calls desperately, trying to re-establish contact.

On board the satellite, his voice can be heard clearly but is being ignored... because the Director has returned. He is angered that his orders were not carried out due to the Doctor's bluff. Blade, chastened, admits he'd been duped and the Director repeats his order to begin the processing. He chastens the Chameleon in Jamie's form as well for taking orders from Blade.

The Doctor tries to persist in his bluff but he's dealing with the Director now and he is unimpressed. The Doctor is moved toward a sophisticated version of the processing equipment in the medical centre, located along one wall of the office. The Doctor begins babbling chattily about Blade's impending disintegration, apparently stalling. However, what's he's really doing is distracting "the most intelligent beings in the universe" while he tampers with the processing equipment. By the time he is forced to be silent, he is finished and the machinery explodes.

The Director is furious and lashes out at Blade. However, a new unit is readily available and the Doctor's fate has only been briefly postponed.

Back at Gatwick, Jean and Samantha have started their own search of the airport car park. They are on their own, growing more desperate by the moment. Unfortunately, they are not alone in the car park. Forgotten during the chaos, Meadows is now running loose around the airport. He has a vested interest in finding the originals himself, certain his life is in danger if the humans find them first.

He has come upon the women in the car park and shadows them, seeing their fervour and hoping they are close to their goal.

A short time later, the new processing equipment is ready in the Director's office. The Doctor is hooked up to the machinery, as is Nurse Pinto. Two Chameleons in their normal faceless state are also placed in the machine. Arm bands are put in place to begin the process.

Meanwhile, Samantha and Jean have had success. They have found one of the car numbers. Hidden inside the car is the body of Immigration Officer Jenkins. They have done it!

Suddenly, Meadows attacks the two women, desperate to stop them from interfering with his own original. Jean and Samantha fight back admirably. Shortly they are joined by policemen who help to subdue Meadows. There is still much to do.

Back on the satellite, all the equipment is in place and the Director is ready to complete the processing. But it is halted again when Jamie reports an incoming message from Gatwick Control, again stating that they have found the originals. Angrily, the Director orders him to ignore it.

The Commandant, however, has anticipated this and knows that a demonstration is necessary to get their attention.

In the car park, all 25 originals have been found and removed from the cars. They are laid out on the ground now, under the eye of the police. At an order from the Commandant, one of the officers pulls the white arm band from the first person in the queue. It is Jenkins.

On the satellite, the Chameleon who assumed Jenkins' identity suddenly disintegrates in the midst of the Director's office. Blade grasps the significance immediately and is frightened and angry. He turns on the Director. The Director tries to deflect him, saying it could have been an equipment failure that killed the false Jenkins, but that story does not wash. The Doctor puts fuel on the fire by repeating his threat to disintegrate them all. Of course, he reminds Blade, the Director will be spared this fate....

The needling works on the spooked Chameleons. Blade wants to re-establish contact with Gatwick, against the Director's orders. Blade, along with Spencer, draw their guns. Shocked that his leadership is being questioned like this, the Director can only watch as Jamie activates the radio and contacts Gatwick.

The Commandant's voice is full of confidence as he replies, telling the Chameleons exactly where the originals were found. He vows to eliminate Captain Blade the same way as Jenkins if he does not hear from the Doctor immediately.

Blade considers this for a moment, and then orders the Doctor released. The Director protests but Blade points his gun and repeats the order. The Doctor is released but refuses to go to the microphone until Nurse Pinto is released from the machine as well. Blade becomes more nervous by the second, certain his life will be ended. To his immense relief, the Doctor goes to the communications unit and responds to the Commandant.

It is enough for the Commandant to hear that the Doctor is alive and well. The Doctor tells him to stand by while he negotiates with the Chameleons. The Doctor tells the Director that he will guarantee the continued existence of his people if all of the young people are returned unharmed. The Director tries to bluff, saying that the miniaturisation process can only be reversed with equipment on their home planet. Blade, knowing that the Doctor is serious in his threat, reveals the lie. The planes can easily return the young people to normal size. Blade is saddened to learn that the Doctor must return his people to their former faceless state, but he realises that life that way is better than death, and that is all that awaits him if the terms are not accepted.

Speaking for the Director, Blade agrees to the terms. Spencer assents, as do others in the room whose originals are in danger on Earth. Enraged by this capitulation, the Director reacts with great anger. He attacks Blade, trying to regain control, and Blade is forced to shoot him down. Jamie joins in and he too is destroyed.

Blade is now in charge, saddened and racked with guilt over everything he has done to the humans and to his own people.

In the silence that follows the deaths, the Doctor goes to the radio and contacts the Commandant, telling him to leave the originals as they are for the time being. They have won. The Doctor's overriding concern is to find Ben, Polly, Jamie, and Inspector Crossland. Blade agrees to help. Certain he can now trust the Chameleons, the Doctor signs off of the radio and agrees to go with Blade to search for his friends.

Back on the ground, the Commandant is confident that the flap is over and the airport can get back to normal now.

Blade takes the Doctor to a storage room near the Director's office. In it are several boxes in which sit the originals of personnel on the satellite. The Doctor opens one after the other until he finds Jamie. Because his duplicate is now dead, Jamie is already conscious and recovering. The Doctor is pleased to see him but dodges his many questions for the moment. Jamie's a bit concerned over Blade hovering in the doorway, but the Doctor assures Jamie he is now a friend.

The Doctor finds Inspector Crossland, also conscious, and helps him out of his box. All that's left is Ben and Polly.

Some time later, the first plane is ready to leave the station and return to Earth. Jamie is aboard, along with the miniaturised Ben and Polly and many other young people. They will be returned to normal size on the journey back. The Doctor and Nurse Pinto are going along on this flight as well, but Inspector Crossland is going to stay to help "tidy things up". He has taken de facto charge of the return operation.

Captain Blade is still in his human guise, but he knows that this will not be for much longer. As the Doctor leaves, Blade asks him - somewhat plaintively - what the future will be for his people. The Doctor is firm but not unmoved by their plight. He tells them that they will be able to return to their own planet, so long as all the kidnapped humans are returned, but that their scientists will have to find some other way to solve their problem. The Doctor offers to give them "one or two ideas" to help out, but that is all he can do.

Blade accepts this silently, his thoughts unreadable.

Some time later, the Doctor, Jamie, and Samantha are back in the Commandant's office to say goodbye. It is a bit difficult as the Commandant and his staff have their hands full with restoring the airport to full operation, but he is nonetheless glad to see the strange little man back safe and sound. He can only imagine the adventure the Doctor has had. In between phone calls, the Commandant bids the Doctor and Jamie goodbye. The Doctor must work to get his attention regarding the police box that was taken from the runway. He needs to get it back. The Commandant puts Jean in charge of this and goes back to his phone call.

Jamie spots Samantha waiting nearby for her brother and goes to say goodbye. It is an awkward moment, full of affection both hidden and revealed. It ends with Samantha giving him a quick peck on the cheek and Jamie blushes. He still can't bring himself to say goodbye right away, but he knows he must go...and that he'll never see the brave girl again. He finally breaks away and heads off after the Doctor. Samantha watches him go, a bit sadly.

The Doctor and Jamie are transported in style to hangar number 4 to collect the TARDIS, in the Commandant's private car. Ben and Polly are with them. Their reunion has been joyous and all seems well as they exit the car near the hangar.

The Doctor immediately heads off behind the hangar to check and see that the TARDIS is there. Polly and Ben are a bit upset at the Doctor's keen interest in leaving. They would like to stay around in London a bit - it has been some time since they've been there. Ben calls it "normal" - someplace he understands. Jamie for his part is ready to go but Polly thinks that 1966 is just fine.

Ben is taken aback by Polly's words. He hadn't realised it was 1966. When the Doctor tells him the exact date is July 20, he is well and truly stunned. That is the exact day that they left with the Doctor in the TARDIS from Fitzroy Square what seems like such a long time ago. Polly realises what he's saying and echoes his sentiment. If they were to stay here now, it would be as if they never went away at all. There would be no disruption in their lives.

The Doctor is saddened to see the excitement on their faces. It is clear that they want to stay, even though Ben says they will come with him if the Doctor really needs them. But the Doctor cannot begrudge them the chance to return to their own world and time so easily. He says quietly that he never got back to his. He is happy for them and gives his blessing. He is certain that Ben will become an Admiral and Polly... Well, Polly will look after Ben.

Emotions mix in Ben and Polly - they are both happy and sad. Polly fights off tears as she hugs the Doctor and Jamie goodbye. Jamie promises to look after the Doctor as he shakes Ben's hand. Ben shakes hands with the Doctor and hopes they will see each other again...sometime. Then the two young people pile into the Commandant's car and ride away, leaving a trail of memories behind.

Jamie and the Doctor are both sad to see them go but pull themselves together. The Doctor heaves a sigh and tells Jamie that they have some work to do. He didn't tell the others, but when he looked round the back of the hangar, he did not see the TARDIS. Somehow, it is gone from its storage place.