A space station called Think Tank six men in white suits are against a hexagonal unit where a giant round silver device sits. One man, the scar faced Skagra opens his eyes. A monitor starts to countdown and the devices seem to stir the other five men into a frenzy. Skagra gets up and moves to some equipment on the walls. After he flips a switch, the men stop their fits and he moves to another control unit. A recorded message states the Foundation of the Study of Advanced Sciences is under quarantine. No one should approach. Skagra leaves the room, the men having a fit again. Soon, the men rise, zombie like and one passes out while the others move around as if in a trance. Skagra leaves in a spaceship.

Chris Parsons, a post graduate student, rides a bicycle towards St Cedd's College, Cambridge. Checking his directions, Chris stops two men and asks where Room 314 is. They direct him to it, past two students and a professor. Chris goes inside.

A white haired, bearded man is in his study in 314 where the TARDIS sits in the corner. The man, Professor Chronotis doesn't seem too concerned with it. He goes to the kitchen but comes back. Chris enters and meets Chronotis, telling him they met at a faculty party a few weeks ago. Chronotis mocks the parties, old dodgers talking and not listening. Chronotis tells him that time doesn't matter at his age and he doubts Chris will get to his age. Chronotis tells him that the last master of the college died when he was run over by a coach. When they met, Chronotis promised Chris could be leant some books on carbon dating: 3rd shelf down or was it the 2nd shelf down? He tells Chris to take what he wants. He prepares tea for Chris. Chris seems startled when the Professor asks about his taking sugar. Chris declares he will be late for a meeting but before he goes he asks about the TARDIS and where the Prof got it. Chronotis thinks it must have been left by someone when he was out. Chris leaves, Chronotis sits and reads THE TIME MACHINE by HG Wells. The Doctor and Romana are in a punt on the river Cam near the college grounds. The Doctor talks about Irwin Chatwick, Rutherford, Andrew Marvel, Chris Smart, Judge Jefferies, Wordsworth: some of the greatest labourers in the history of Earth. Romana mentions Newton, who invented punting. The Doctor thinks Newton was unlimited in his genius. Romana thinks the punt is primitive and simple. She loves the spring and the leaves. The Doctor mentions it is October. She thought he told her that they were coming her for May Week. He did: May Week is in June. Romana is confused and the Doctor mentions so is the TARDIS, "Ha Aha." She loves the autumn. Nothing can go wrong. No coordinates, no dimensional stabilizers. The Doctor marvels at the punting: just a strong pair of hands. The Doctor drops his pole and thinks it is time to go see the Professor back in his room. As they pass under a bridge that Skagra is standing on top of, Skagra puts his hand over a carpet bag he is holding. A strange sound and the babble of voices occur. Romana hears the voices.

Chris goes out of his lab and checks some equipment. He takes out the books he borrowed from Chronotis. He looks at two of the books but a third is in a strange text written in a totally unknown alphabet. The texture of the paper seems odd to him.

The Doctor and Romana arrive back at the college where the Doctor cannot recall who founded the college and other facts that escape him. The Doctor tells Romana she should have been a historian when she recalls the correct name: Cedd. She comments she is a historian as the Doctor goes to Wilkin, the jolly porter at the Porter's Lodge. Wilkin greets the Doctor with, "Good afternoon, Doctor", remembering the Doctor. Wilkin recalls the Doctor was given an honorary degree in 1960. Wilkin knows he wants to see Professor Chronotis, who returned a few moments ago. The Doctor asks how he knew he wanted to see Chronotis. Wilkin states, "Because that's who you asked for in 1964, 1960, and 1955, sir." The Doctor says, "Did I really? I was here in 1958." Wilkin asks if he was. "Yes," the Doctor smiles, "But in a different body." He hands Wilkin the pole from the punt and leaves. Romana is standing away from them and asks the Doctor to come on, staring outward. The pair go into Professor Chronotis's study and the Doctor mentions to Romana that the Prof will ask if they want tea, which he does. The Doctor will take two lumps and two sugars. Chronotis greets the Doctor as an old friend. He meets Romana for the first time, "I've heard so much about you." The Doctor asks, "Have you really?" "Not yet but I will have done," the Professor states, sitting. Through his glasses, the Professor tells them that when Time Lords get to his age, they tend to get their tenses mixed up. He asks them if they want biscuits. "Well, I wouldn't have said no," the Doctor answers. "Crackers?" "Oh, sometimes," the Doctor nods.

In his white outfit and cape with a white hat, Skagra walks the streets of Cambridge while carrying his large bag.

Chronotis has been in these three rooms ever since he retired from Gallifrey... some 300 years. Everyone is discreet and nobody noticed. Chronotis asks, "Well now, Doctor, young fellow, what can I do for you?" The Doctor mentions that he sent them a signal to come as soon as possible. He never sent the signal but is delighted to see him. The Doctor, eating another cracker, wonders who sent the signal.

Skagra walks past the porter Wilkin and calls him over, "You," a few times, arrogantly and in a posh manner. He is treating him badly. He asks for Chronotis. Wilkin tells him that he is with a very old friend, the Doctor.

Chris tries to cut the book with a razor but cannot. He takes it to the Spectrographic Analyser but the book just makes the device smoke and burn out.

Chronotis tells the Doctor and Romana he knows who sent that message -- him but he sent it a long time ago. "I told you you got the time wrong," Romana states to the Doctor. The Doctor says, "You're always saying that." "You're always getting the time wrong," she smiles. Absent minded, Chronotis asks what was what about when the Doctor asks about the message. The Doctor explains about the strange babble of inhuman voices... but the Professor thinks that was just undergraduates talking to each other--"I've tried to have it banned." The Doctor thinks it sounded like ghosts. Romana thinks it sounded like screaming. She turns away when he talks about a delicate matter. Chronotis tells the Doctor it was about the book.

Chris has the book under an old X Ray machine as he moves behind a shield window. The book starts to glow so Chris switches the machine off. In protective apron, he moves to the book but recoils as if it were burning him when he touches it. He burned his hand.

Skagra is in the streets. He watches a man emerge from a shop and go to a car. He asks the man for a ride and the man gives it to him. Skagra opened his bag and the sphere attached itself to the driver's forehead. The driver passes out and the car stops. Skagra takes charge of the car... while this happens the sphere has voices emerge...which...

The Doctor, Romana and the Professor hear again. Chronotis mentions the book he was talking about -- a book he says he accidentally took from Gallifrey. They are looking for the book now. Chronotis admits he loves his books and didn't take it by accident--he took it for study. He called for the Doctor, thinking the Doctor would take it straight back home to Gallifrey, now that he is retired Chronotis is not supposed to have a TARDIS. The Doctor doesn't want to be critical but he will: it is dangerous and risky to bring back books from Gallifrey -- these books could be dangerous in the wrong hands.

Chris calls a colleague, Clare Keightley and tells about the book. He invites Clare over to see it for herself, telling her he doesn't think this book is from the Earth!

The Doctor reads from a book called The Victim by Saul Bellow, which Romana recognizes, "On some nights, New York is as hot as Bangkok." The Doctor reads, "Once upon a time," but throws the book, "Read that." He finds another book, "Ahhhahh, huh and in the ancient days of Rassilon, five great principles were laid down, can you guess what those were, children?" Romana calls it a Gallifreyan Nursery Book, she had it when she was Time Tot. He thinks it is very good. The Professor is on a ladder looking for the book, that one is just a memento. The Professor sees another one but puts it back, checks another one, that is not the right one either. The Doctor asks how many books he brought back, for Heaven's sake! "Just the odd two or seven." There was just one book that was in any way dangerous.

Skagra drives to a deserted field not far from a farm house and farm. He walks to the empty field and seems to walk up an invisible ramp into an invisible spaceship.

The Professor, Romana, and the Doctor are looking through more and more books. Romana asks what the title is. When the Professor tells her The Worshipful and Ancient Law of Gallifrey, the Doctor drops the book he was holding. It is a 5 by 7 red book. The Doctor angrily asks how it got out of the Panopticon Archives -- Chronotis just took it. There is no one interested in ancient history on Gallifrey any longer and he thought certain books would be safer with him. The Doctor asks if they were. "Yes in principle," Chronotis states. The Doctor wants to talk to him on yet another delicate matter, lifts him bodily off the ladder he is on, and takes him aside. That book dates back to the days of Rassilon--it is one of the artefacts. The Professor acts as if he didn't know that but the Doctor notes that the Professor knows that perfectly well. Rassilon had powers and secrets that even they do not understand. They hope no one else can understand it. The Doctor mentions to Romana to find a little book, and she heard it is 5 by 7 and red. "Could be green," Chronotis calls to them. They look back at him in bemusement.

Romana finds Roget's Thesaurus. The Doctor finds the British Book of Bird Life in colour. Romana finds the book Alternative Betelgeuse and Wuthering Heights. The Doctor finds a book that recommends Tandoori chicken for starters and the Time Machine. Romana finds Sweeney Todd. The Doctor explains the artefacts are imbued with tremendous power. Romana recalls the words used at the Academy induction ceremony, "I swear to protect the Ancient Law of Gallifrey with all my might and brain. I will to the end of my days with justice and with honour temper my actions and my thoughts." All words and no actions, the Doctor states. Romana doesn't think that is true: what about Salyavin. The Doctor recalls Salyavin was one of his heroes. Romana calls him a criminal and asks if he realizes his hero was a criminal. "Criminal yes, but he had such style! Such flair!" "Panache," Romana puts in. "He was a bit like me in that respect," the Doctor says. Romana asks if he ever met him to which the Doctor takes offence and yells. He asks the returning Professor if he ever met Salyavin, a contemporary of his. The Professor comes running in and tells him he just remembered but the Doctor remarks he only just asked about Salyavin. The Professor remembers not that but that a young man who's name he cannot remember was here...the Professor cannot remember what his memory is like...something you strain rice in...but then he does recall he has a memory like a sieve. "A, A, no it doesn't begin with A..." Chronotis ponders, "B...B...BB...?" Romana and the Doctor both ask, "C?"

Clare is with Chris in his lab. The text looks like a cross between Chinese and algebra. There is not a polymer in it or a crystalline structure within it. Half of it is stable all the time but the other half is not stable at all It behaves like a super conductor one minute and blows up the equipment the next. Clare thinks Chris should go ask Chronotis what it is and he leaves her there.

The Professor gets to X and Y trying to recall the name of the boy. It is Y for Young Chris Parsons that jogs his memory, "Born 1951, graduated 1975, Honours Degree in Chemistry, currently engaged on Post Graduate studies in Sigma Particles." He should be in the Physics Lab. First left. The Doctor tells the rushing off Professor (rushing off to make tea) that he will be back in two minutes but then he whispers to Romana if he is not back in two hours, she and the Professor should lock themselves in the TARDIS and send out an all frequency alert and wait. After the Doctor leaves, Romana tells Chronotis she will take two lumps with tea but no sugar. Skagra enters his invisible ship and puts on a jacket and tie, gaining approval from the ship. He picks up the carpet bag and tells the ship he is off to retrieve the book. He seems to come out of nowhere as he leaves the ship and moves into the field. He goes to the car.

Borrowing a bicycle, the Doctor speeds toward the Physics Lab. He nearly collides with another on a bike: Chris.

Skagra reaches the college again and leaves the car. He walks the grounds and meets Wilkin. He asks if the Professor is alone. Wilkin tells him the Doctor left a few minutes ago.

Chronotis is upset: they've run out of milk. Romana is shivering from a feeling: those voices unnerved her. Romana doesn't think the Professor should run out and get some milk, short of having a cow he doesn't know of any way to get milk. Romana opens the TARDIS doors: she and the Doctor have plenty of milk. The type 40 TARDIS came out when he was a boy and he tells her the kitchens are too far from the console room but Romana tells him she has never known the Doctor to use them. Romana goes in. Salyavin, the Professor chatters to himself, "Good riddance to him." A knock on the door and the Professor, back to making tea, tells whoever it is to come in. He will have to have lemon with his tea, whoever it is. It is Skagra and he comes in accompanied by voices when he opens the carpet bag. "How many of you are there, for Heaven's sake? I only have 7 cups." He hears the voices and thinks it is a crowd of guests. Skagra gets to the point: he wants the book. Chronotis tries to make as if he hasn't got any books... or the book that Skagra wants. Skagra knows about the book and the Panopticon. Chronotis tells him he doesn't know where the book is. Skagra opens the bag and the silver sphere attaches to the Professor's head and he falls.

At the lab, the Doctor meets Clare and picks up the book. Clare asks about the book and why it makes the equipment explode.

Romana leaves the TARDIS with some milk and K9. She finds the Professor on the ground. Chris Parsons comes in. K9 ascertains the Professor is not dead but in a deep coma. Romana meets Chris and figures out he had the book and asks about the Doctor. K9 denotes that the Professor has been subjected to psycho active extraction. Chris thinks K9 is neat. Part of the Professor's mind has been stolen and his resistance to it has caused severe cerebral trauma. Romana tells Chris to get the medical kit from the TARDIS. "First door on the left, down the corridor, second door on the right, down corridor, third door on the left, down the corridor, fourth door on the right, and fourth white cupboard opposite the door on the shelf." Chris enters the TARDIS and comes out again, stunned. Romana asks him to hurry up. She tries to get the Professor to hear her. Chris comes out again soon enough. Romana puts a collar over the Professor's neck. The collar will take over the automatic brain functions. Chronotis is breathing and his hearts are beating. His eyes are open. Chris tells her the human mind doesn't work that way... but Romana shakes her head, oddly telling him, "The Professor isn't human..."

The Doctor mumbles to himself that the book must have stored vast amounts of sub atomic energy which was released when the spectrograph was turned on. The book tells him nothing so he figures it is not a book at all. The carbon dating test teletypes a message to them. The book is 20 thousand years old. It is minus that amount of time. The Doctor finds out it is having time run backwards over it. He must return it to Gallifrey at once.

In his ship, using the cone and the sphere and other devices, Skagra saw into the Professor's mind, see the arrival of the Doctor and Romana, and soon he sees the student that came to borrow the book but he couldn't see through the distortion to see Chris's face. The Professor's mind, trapped in the sphere, can be tapped but even so, the Professor can resist him and this process. When Skagra orders the sphere to find all info on the book and its location, the picture breaks up. Skagra calls the Professor brave but the resistance will almost certainly prove fatal.

Chris ponders on the Professor's fate and the impossible is all around him now and that Romana is not from Earth. K9 finds some slight conscious thought in the Professor but the condition is terminal. The speech centres of the brain are inactive. Romana hears something and K9 is ordered by her to extend his antenna to the Professor's heartbeats...the Professor is beating in Gallifreyan Morse code! He beats beware the sphere, Skagra, beware Shada. The secret is in the..." K9 tells her the Professor is dead.

Before it can do anything, it moves back from the sound of the appearing TARDIS. Romana pops out of the doors and calls the Doctor who shhs her and runs inside. K9 had traced the sphere after it attacked the Professor. The Doctor realizes he dropped the book but goes into deep thought to control the TARDIS to pick it up even after K9 and Romana reveal the Professor's mind was stolen by the sphere.

The teletyper attached to the X Ray machine in the Physics Lab comes to life and stirs Clare a bit. She has fallen asleep over a bench.

Chris watches over Chronotis but his hand goes through the Professor's body and Chris soon sees the body vanish. The TARDIS appears with a strange pop. The Doctor sternly exits and asks Chris who he is and when Chris tells him, he tells Chris that he is the one causing all the trouble. Chris explains about the Professor disappearing into thin air. The Doctor thinks the Professor must have been on his very last regeneration. Chris and Romana tell of the three things the Professor said before he died. Shada seems to mean something to the Doctor but he cannot recall what. The Doctor vows to have a little chat with Skagra since this man or whatever he is, killed a very old friend of his. The Doctor asks K9 to find a trace of the sphere. It is too weak to get a bearing but the Doctor and Romana will wait in the TARDIS until K9 can trace it again. The Doctor calls Chris by the name of Bristle, telling him to wait with them in the TARDIS.

On its way back to the spaceship, the sphere passes near a man on the river bank. The man is fishing and has an umbrella and fishing rod. The sphere attaches to the man's head and the man falls into the river after it steals his mind. The man falls face down into the river...

Clare is woken up by the teleprinter. She tears off the text and rushes out, taking the university directory with her. She is looking for the Professor's rooms.

K9 alerts the sleeping Doctor, Romana, and Chris. He has tracked the sphere.

Clare finds the Professor's room.

The sphere moves through the fields and pastures toward the spaceship as the TARDIS arrives and the Doctor, with hat on, emerges. Romana and Chris are not far behind. They see the sphere enter an insiviable ship. The Doctor watches, "Did you just see what I didn't see?" "No," Romana answers. "Neither did I," the Doctor commands but Chris confirms what the Doctor did see. The Doctor moves off to a cow path.

The sphere reports to Skagra and tells him the Doctor has escaped and is approaching their ship. Skagra asks the computer to give him info on the Doctor and the TARDIS. It identifies the TARDIS as type 39.

The Doctor walks into the side of the ship but warns the others not to move. The Doctor calls K9 a stupid animal that he didn't tell him that the ship was here. K9 assumed they could see it. The ship's functions are beyond K9. The Doctor asks what powers it and K9 tells him insufficient data. The Doctor comments, "Aren't we all." It should keep the cows guessing. While the Doctor tries to find a way in or a clue to where the entrance is, Chris asks what that red carpet is doing here. The Doctor follows suit and asks the same thing. The Doctor moves and hits another object but finds the way up. Skagra is watching their movements on his screen. He allows the door to open. They see the entrance and the interior of the ship floating. They go in. A cube of light surrounds Romana, K9 and Chris and they vanish. The Doctor turns around and finds Skagra standing there.

Clare finds Chris's satchel and the scattered books. She hurries out of the room.

The Doctor confronts Skagra about the Professor and the Book but Skagra takes the Doctor to his control room, telling him they have more important things to discuss. He tells the Doctor his companions will come to no harm. Skagra was just interested in the Professor's mind.

Skagra shows the Book to the Doctor and attempts to get the code to the Book's text from the Doctor. The Doctor refuses so Skagra gestures to make the sphere attack the Doctor and it does. The Doctor falls back in his seat.

Chris figures he and the other two were matter transferred to this white room which is shielded. Romana tells him that is very clever. She knew it the whole time. Chris was supposed to deliver a paper to the astronomical society that night, planning to disprove the possibility of life on other planets. Chris mentions the curious wall and Romana, not listening, says, "Blast it," in reference to something else and K9 blasts the wall. The ray ricochets around the room. They duck. The wall is blast proof. K9 picks up the voices and informs them the Doctor's voice has been added to the babble.

Clare bumps into Wilkin, running from the building. Clare explains the book is very dangerous and Wilkin doesn't understand at first but then seems to. They both, separately, plan to find the Professor. Wilkin says, "I don't know, nowadays they will publish anything."

K9 picks up on signals on any frequency. Romana wishes she can get out of the room and vanishes in a cube of light. Chris does the same thing -- wishing he and K9 can get out of the room. He says, "Blast," when it doesn't work for him but stops K9 from firing another blast.

Romana appears spinning in the hall of the spaceship, the cube dropping her out of it. She is stopped from spinning by Skagra who grabs her by the arm and takes her out of the ship. He is in his white outfit and hat again. The sphere follows them out.

Chris wonders how Romana got out but not he. Chris gets mad at K9's insufficient data.

Skagra takes Romana to the TARDIS and uses the Doctor's key to get in. The Sphere enters with them. The TARDIS slowly vanishes as he uses the Sphere to control the TARDIS.

Clare is looking through the Professor's desk draw. She searches a shelf and finds an old but large key. She uses it to open an old wooden cupboard and accidentally presses a control which flips. The interior looks futuristic with metallic control panels. Clare activates it and a large flash occurs. There is a small blast and she falls over the desk. The room shudders and drizzles. Clare is knocked out.

Wilkin knocks on the door of the Professor's rooms. He opens the door, expecting to find Clare but instead he sees a blue twinkling void! He turns away in shock.

Chris and K9 are still in their white, silver, and red cell room. A spinning light cube engulfs them and takes them to the hallway where they find their way to the control room, finding buttons on the wall to open the door. As they enter, the ship returns the oxygen supply to normal. K9 informs Chris that the TARDIS is no longer on board this ship. The Doctor revives and revives the idea that he is dead to K9 and Chris. K9 accepts this but Chris does not.

The TARDIS is en route to a large command ship. Skagra tells Romana he needs Time Lord technology as she pumps him for information about Salyavin -- is Skagra Salyavin?

On the command ship of the Krarg, one wall is a giant screen that shows the galaxy. The TARDIS appears, Romana, Skagra and the sphere emerge from it. A Krarg commander, made of diamond shaped coals is behind her. They are made in coffin shaped vats that are filled heavy gases.

The Doctor, Chris, and K9 come to the conclusion they do not know what is going on. They ask the ship but it claims it does not know much either.

On the Krarg command ship, Romana asks politely why Skagra will not tell her what he is doing. He leads her to the large view screen wall, where he explains the waste of having billions of people on billions of worlds just spinning uselessly through their lives. He compares them to a handful of atoms spinning at random. He tells her the one thing that demonstrates the difference between atom energy is life in humans and other beings. He wants to control all that life from here to achieve. Romana backs away from him but bumps into a Krarg. The Krarg commander tells Skagra he needs more crewmembers. He leaves, followed by Skagra and Romana.

In the Annex, there are vats of heavy gases where Krarg are made. The Commander pushes a button and in a vat is a wire skeleton that starts to glow. Black crystals form around it and soon a full Krarg is pulling itself out of the vat. Romana is less appalled than she is amazed.

The Doctor orders the Ship to take them to Skagra's last position. The ship starts up and begins to launch. Unknown to the Doctor, Chris, and K9, in another part of the Ship, launch procedures have started a gas filled vat. In this vat, a new Krarg is about to be made. The Ship blasts off and becomes visible. The Doctor is again smug about his ability but when he asks the Ship to give an ETA--he finds it will take three months to get there! He orders the ship to stop. The Doctor finds out the Ship is able to self repair itself. He starts to make some remodifications. The Ship's new Krarg is almost complete. It hears the Doctor giving instructions to the Ship via the intercom. The Doctor introduces the Ship to new concepts including switching the conceptual geometer from analogue to digital mode. He also triggers feedback responses up reading of up to 75 dash 839. The Doctor asks the Ship to realign the drive circuits. The Ship shimmers and vanishes from space. The Doctor tells Chris he constructed a primitive dimensional stabilizer by remote control and they can go anywhere in a couple of minutes. He also wants it to reverse the polarity of its main warp feeds. Chris is impressed. The Ship dematerializes and as it does, the sound of a TARDIS is heard.

Clare starts to regain consciousness, having fallen to the floor of the Professor's room. The room has a low hum in it and lots on the console blink. She bumps her head on the small table/desk and sits down near a high backed chair. Up pops Professor Chronotis's head, asking what she has done with his machine! He goes over to the console and checks it. He is wearing a nightgown and a pointed night cap. He asks Clare if she wants some tea.

On the carrier ship, Skagra was using the sphere to delve more into the Doctor's mind to find the secrets which would unravel the Book. On the screen images were thrown up: Clare, Chris, Romana, The Professor, Wilkin, and the TARDIS. One word kept occurring: the Book is the Key with which the Time Lords imprisoned their most feared criminals. Skagra seems pleased when he finds out that Time was the forgotten element of the equation.

On the Ship, the Doctor and Chris settle down for the trip with some idle banter. They are unaware of the fully formed Krarg heading down the hallways at them.

The Doctor and Chris are annoyed at the slowness of the trip anyway. They forget this when the Krarg bursts through the door and enters. The two men try to get to the door, rounding past it but the Krarg identifies them as intruders and raises a gun. K9 retaliates and stops the Krarg but as soon as K9 stops firing, the Krarg, only affected when K9 fires, continues to move. The Doctor removes K9's inspection cover as Chris pulls a power feed from the wall and hands it to the Doctor. The Doctor connects it to K9 so this time the robot dog can hold the Krarg off for a longer time. The Ship announces docking will commence at the Think Tank space station.

Chronotis brings tea on a tray to Clare. He tells her he is, am and will be Professor Chronotis. The Gallifreyans have never come up with a proper form of grammar to cover this situation: timelessness. His room, standing obliquely to time, is a very ancient TARDIS which he rescued from the scrap heaps. He wasn't allowed to have one really. If he didn't, he would still be dead. Clare's mishandling of the controls meant she tangled with his time fields at the critical momenta paradox within an anomaly. She doesn't understand him. He tells her they must get the book, the key to the prison of the Time Lords -- Shada. Time Lords have been induced to forget about Shada. If Skagra gets there, to Shada, he can go there for one reason and they must stop him. Clare stands up, "Yes!" Then she wonders why. She asks the Professor this as he walks out but pops back in. He tells her it is a matter of who is there, not what.

Skagra reviews the Doctor's last few hours before his "death" via sphere. He takes Romana and the sphere back to the TARDIS. Chris and the Doctor leave K9 in control of the Krarg. They go out to Think Tank, hearing the “Do Not Approach” warning. They emerge from a shuttle bay. Chris tells the Doctor they cannot travel faster than light, Einstein. The Doctor is amazed when Chris claims to understand Einstein and quantum particle theory. The Doctor continues to ask names of who Chris understands: Newton, Prank, Shronberg. Chris does. The Doctor tells him he has a lot to unlearn. They find a sign which has the Institute for Advanced Science Studies logo on it. Chris sees smaller letter and wonders if they mean Advanced State of Decay. The Doctor hears something and he and Chris wander into a main control area. The Doctor identifies it as Think Tank. He stops short as he starts to explain to Chris -- for he spots five ghostly figures shivering in fits. The five notice them and begin to move toward them, haggard, old, grey, pathetic animated cadavers... moaning and rumbling...

In the TARDIS, Skagra stops turning the book and notices that the console rotor stopped moving. He realizes time is running backwards over the book and that turning the last page will take him to SHADA.

The five men are not harmful. The Doctor examines one of the men. Chris asks what the five figures are. Victims of Skagra's brain drain. The Doctor stares as he thinks their memory patterns might remain. He sits down and questions and comments from Chris make the Doctor realize something himself: he asks Bristle if he can do something for him and when Chris eagerly tells him yes, the Doctor claims it will not be pleasant. "Oh," Chris says.

At the command ship, Skagra returns to the control room and tells the Krarg commander that they will prepare for entry to Shada. He tells Romana that she should prepare to meet one of the most powerful criminals in history... Salyavin.

The Doctor carries an old man, one of the victims to the console. He will give access to Chris's intelligence. Chris hopes the Doctor knows what he is doing. "So do I," the Doctor states. The other men cower in the corner. Dr. Caldera is the name of the man attached to Chris's intelligence reserves. The Doctor finds this out when he activates. Chris passes out but the Doctor puts his head on Caldera's chest to see if he is alive. As he does so, a clawed hand rises -- the man's nails are very long and approaches the back of the Doctor's head. The Doctor draws back but the man, Caldera, says the name, "Skagra!" K9 is having trouble holding off the creature: its strength is growing.

Dr. A. St John D. Caldera gives the Doctor his name, one of the famous neurologists of his generation. He also tells the Doctor the names of the others: AST Thira, psychologist (the Doctor touches the man's arm); GV Snatori, parametricist (the Doctor pats the man's bald top head), Dr. LD Ia biologist (the Doctor pats the man's cheeks), and Professor RF Akrotiri (the Doctor just waves and then raises a fist to the man), unspecified... and Skagra, geneticist, astro engineer, cyberneticist, neurostructualist and moral theologian. The Doctor thinks he is too clever by -- seven eighths. The men do not who Skagra is. Think Tank was Skagra's idea. Pooling of intellectual resources by electronic mind transference. The men did not know how grand Skagra's scale would be. They built the sphere and Skagra stole the men's brains. K9's blaster ray was fused into the haze around the Krarg. Caldera tells the Doctor that Skagra's plan is to get one unique mind -- Salyavin. Caldera passes out. K9 retreats. Worried, the Doctor wonders if Bristle is dead and asks if he is all right. Chris tells him he feels marvellous. The Doctor says, "Good, good, it will pass." He has learned enough to frighten him out of his wits. Caldera soon joins the other scientists. K9 comes in and soon the glowing Krarg follows. Its footsteps leave a smoking trail. It moves an arm into a wall and the wall burns. K9's power is almost depleted. The Doctor tries to get the scientists away from it but he has to duck back away from it. It moves at the Doctor, missing and hitting the console, blasting it.

The Doctor frowns at the monster but asks Bristle (Chris) if he is still feeling marvellous. Chris is and the Doctor wipes his mouth with his arm and tells Chris to give him ten seconds. The Doctor runs to the scientists as Chris challenges the Krarg. The thing moves at the Doctor, who blocks the scientists from it. Smoke fills the room as K9 reports danger over and over. The monster somehow manages to electrify the old men but not the Doctor. Chris uses the Doctor's scarf to pull him out of the room into the hallway through thick smoke. Chris helps him run the right way--the Doctor seemed to want to return to the room to help the old men. The old men seem to be killed by the monster but they are still moving.

The Doctor finds the hatchway back to the Ship jammed. He uses the sonic screwdriver to open it. With the Krarg just behind K9, they three make it to the Ship. The Doctor orders the Ship to dematerializes and seconds after it does, Think Tank explodes into a mass of spinning metal on fire.

The Doctor questions the Ship again but gets no info. He then asks if Skagra has a home. When the Ship tells him Skagra does, the Doctor orders it to take them there. The Doctor smiles at Chris, telling Chris he does so hate computers, they are so literal. The Doctor asks K9 to confirm this but K9 just says, "Master?"

The Professor is wearing a hat and is fully dressed and working on some equipment in his TARDIS rooms. Clare is also working on some machinery, not knowing what she is doing. Both wear glasses. Clare's touch to the console was just a spasm which left them jammed between two irrational time interfaces. Time is moving away from them and they have to disentangle themselves. If they do manage to free themselves, the Professor will have to be careful: he may cease to exist again. Clare takes off her glasses and starts eating. He tells her to do as he does: forget about it all. She thinks it easier said than done. Clare asks about this Salyavin person. The Professor tells her a criminal hothead whose exploits were exaggerated but he was brilliant and had a peculiar talent. Clare asks if she can help him with the device he is making. She can learn and claims she is very quick. He goes to get a wrench. The device they need to repair is difficult: an interfacial resonator which needs two operations which must be performed simultaneously. He takes his glasses off and points with his wrench. She must never speak of what he is about to do. He makes her promise, sternly. He will do this but never do it again. His eyes glow green and he stares at her. After the stare she knows all the machinery and the operations they are about to perform! She knows she holds a conceptual geometer relay with an agronomic trigger and a defunct field separator but they can dispense with it if they can get the interfacial resonator working properly.

K9, Chris, and the Doctor materialize with the Ship onto the Krarg carrier craft. The Krarg commander watches as a new Krarg rises out of the vat. The Commander goes to report to Skagra.

In the main control room, Romana is kept under guard of a Krarg who has Romana sitting in a corner. Someone taps her on the shoulder and she turns to see the Doctor. Amazed, she asks how he got here. He tells her that these nice people brought him...behind him is Chris, K9 and many Krarg! While Skagra is surprised to see the Doctor, the Doctor says hello to him in a friendly manner. The Doctor chides Skagra and his great purpose, "Great purpose! Haha! I know what you want to do, you old slyboots. You want to take over the universe, don't you. I've met your sort before. Any moment now a mad gleam will come into your eye and you'll start shouting the universe will be mine!" Skagra calls the Doctor limited and the Doctor shouts, "Limited?!" Skagra tells the Doctor he wouldn't want to rule the universe. The Doctor rants, "Exactly! That's what I keep on trying to tell people. It's a troublesome place, difficult to administrate and as a piece of real estate it's worthless because by definition there'd be no one to sell it to."

Skagra wants to fulfil the natural evolutionary goal of all life, "With the aid of the sphere I shall make the whole of creation merge into one single mind, one godlike entity. The universe, Doctor, as you so crudely put it, shall be me!!"

The Doctor says, "Uh...have you discussed this with everyone? Why don't you send one of your Krargs to make some tea, we could sit down and..."

Skagra tells the Doctor to stop his inane witterings. He tells the Krargs to take them away and lock them up and throw away the key. As the Krargs make to take him, the Doctor moves for the TARDIS but is blocked by Krargs. He gets out a door and rushes down a corridor. Chris and K9 manage to follow but Romana is grabbed. Skagra order the trio killed. Krargs follow the Doctor out. Skagra takes Romana and goes to the TARDIS with several Krargs. The Doctor, Chris, and K9 hide in an alcove as Krarg pass by. They emerge from it and start down another hallway, hearing the hum of a TARDIS. A blast from a Krarg gun slams past them. They run another way but find more Krarg. The trio are forced to a T junction and know it is a dead end. The Doctor sees an unusual, old, wooden door and runs through it, Chris and K9 right behind him.

The Doctor comes dashing into the Professor's rooms, followed by Chris and K9. He slams the door shut. Turning he and Chris are shocked. The Krargs try to break in. The Professor asks how the Doctor likes his TARDIS. The Doctor blows on the console, "Oh, Ace, ace, ace." The Doctor calls Chronotis an old slyboots, the best way to hide it is to live in it. Clare and Chris talk but are unsure about what is going on, both in a bit of shock. The Doctor tells the Professor that Skagra is out there and he has the TARDIS, Romana and the Book. He asks the Professor about his being dead. The Professor says, "So did I." "Did you really?" Chronotis tells the Doctor that now that Skagra has those things, he can go to the Time Lord prison planet. He also tells the Doctor he probably forgot about Shada. The Doctor rants, "I never forget anything, I never for...that's right I have forgotten." The Doctor asks Clare to ask him who Salyavin is. He was imprisoned on Shada. He was imprisoned centuries ago and he could project his mind into others' minds. Skagra is doing the opposite, taking minds out of people. He must not get to Shada.

In the TARDIS, Skagra turns the pages of the book and the central column on the console moves in time to it. The key turns the lock open... to open the door to Shada. A deep melodic hum fills the air. The TARDIS moves on.

Clare gives tea to the Doctor and Chris. Everyone is drinking tea. Eventually after thousands of years, Skagra will be able to slowly over this time, put his mind into every organism, every mind in the universe. It would spread like a disease. Every mind working as a single mind...Skagra's mind. The Doctor figures the Professor followed the TARDIS'S space time trail. They could follow Skagra the same way, Professor Chronotis figures. As the Doctor comes to this conclusion, he is about to jump up. The other three do jump up. The Doctor sits down, calm again. They follow suit and sit down. He jumps up again, "Let's go!" He runs to the console and they follow.

A strange looking planet Shada is: all white and brain-like with buildings build into it and a sun close to it. The TARDIS materializes in the small dark reception area of SHADA. Skagra, Krargs and Romana exit. Romana comments that Skagra should feel at home here. At another central device, Skagra finds information he wants: Salyavin; Mind Crimes; Section 7/8; sentence in perpetuity; Cabinet 5, chamber 7. Skagra takes Romana and a Krarg with him and leaves some Krargs to guard the device.

Chronotis tells the Doctor they've arrived. "Good, good, good," the Doctor shouts. He also tells Clare and Chris they have to stay here and shushes their protests -- he is not at liberty to explain. He goes to K9 and tells him to come along and he cannot tangle with any Krargs unless he has to tangle with any Krargs. The Professor hurries out. The Doctor and K9 hurry after him. The Doctor worries that the Professor seemed in some way to know what Skagra was thinking and he takes them in a particular direction. He knows which way Skagra went and bluffs that he heard the footsteps. The Doctor suspects something else.

Revivification systems come on and a few zombie like prisoners are standing about in a frozen state. Skagra enters the main chamber and he wants to free other prisoners before he meets Salyavin, hoping they will be the first to participate in the new universal mind. Going to a console in this chamber, he looks up records of other inmates and sees a Dalek, a Cyberman, and a Kraal. Gas swirls around the inmates he picks.

Chris and Clare talk in the Professor's rooms. Chris thinks it is odd the way some days work out. Clare thinks there is something very odd about the Professor. Chris asks, "Why single out the Professor?" Clare blames Chris for not listening to her. Chris says that just because they are from Earth, doesn't mean they have to be patronizing toward them. He doesn't understand how this all works...Clare tells him she did. It was something the Professor did to her.

The Doctor spots the TARDIS guarded by Krargs and decides to play it the Professor's way and finds Skagra first. Chronotis gives K9 instructions to destroy the sphere if any attempt is made to use it on them.

The trio burst in as Skagra finds the chamber that holds Salyavin but it is too late: the villain has already started to revive the criminal. A Krarg uses its blaster to hold off the Doctor, Chronotis, and K9. In the cell, Skagra finds a dummy, a fake. He asked where Salyavin is. The Professor calmly says, "I escaped centuries ago!"

Chris and Clare continue to talk. Chris tells Clare that the ability to do what Chronotis did to her was unique only to the guy that Skagra has come here to find. Fed up with being left behind, the pair leave the rooms -- the Professor's TARDIS.

K9 fires at one of the prisoners and the prisoner falls. A Krarg lumbers at K9 and picks him up, the Doctor ordering the dog not to fire since it would empower the Krarg as the one before it. Romana, now free from the Krarg, runs as the Doctor shouts, "Run!" The pair collide with a running Clare; the Doctor chiding her for not remaining with the TARDIS. Romana gets K9 back on his tracks and the foursome make their way toward the TARDIS. They cannot get to it since Krargs are all over the hallways. The group make their way back to the wooden door and Chronotis's rooms. They get to it and slam the door behind them. The Doctor orders them to sit down; Romana stares strangely and admits Skagra has beat them on every point. The Doctor shushes them, telling them he is thinking and it's depressing him. All the stolen minds are in the melting pot...and they can control everyone. Romana smiles and stands up and walks away. She reminds him of something: his own mind is in the melting pot too. The Doctor wants her to stand there and he gives her a pin and metal that reads, "I am a genius." He seems to kiss both her cheeks. He salutes her and she salutes back.

Skagra and his band cannot get into the Professor's rooms so they move back to the TARDIS. He plans to return to the Carrier Ship and from there a fleet of smaller craft will depart for selected centres of population. Soon, he sets the TARDIS to dematerialize.

The Doctor has formed a very dangerous plan. He calls it a touch dangerous but Romana corrects him -- he stands about as much a chance as... well there is nothing he stands as much a chance as since it will be terribly dangerous. The Doctor tightens his scarf, "Well, I'll have to be very brave, won't I." Romana chides him, "Doctor, it's isn't funny!" The Doctor grips her shoulders and arms, "Listen, I can do your part if you can do mine...you're a hero, remember." The Doctor tells Clare to hold on very tight.

In TARDIS, Skagra realizes something is very wrong.

Romana and the Doctor hit switches and the Doctor tells Clare to hold tight again. The Doctor, Romana, and Clare travel in the college rooms TARDIS of Chronotis while Skagra, Chris, the Krargs, and the prisoners are in the Doctor's TARDIS. Both are travelling in the Space/Time Vortex. The Doctor is generating a forcefield which snares Skagra in TARDIS. Skagra opens the shutter screen in the Doctor's TARDIS and on the viewscreen he observes the college rooms floating as one in the time vortex. In the College Room TARDIS, the Doctor says, "Clare!" Clare says, "Yes, Doctor, I'm holding on." The Doctor says, "Come over here and hold onto this then." Clare obeys.

Clare holds a long switch down--it looks like a telescope. The Doctor tells her whatever she does not to let go. As she and Romana struggle at the controls, the Doctor gives a speech, holding a large fork like tool used for stoking coals in a fireplace, "And 23rdly, out there in the space time vortex, time and distance have no meaning, but here in this little, little room..." Romana yells at him to get on with it. The Doctor instructs her to switch off the vortex shields as he showed her, just one little bit of timelessness. She finds it difficult and the tea trolley moves. He yells at her to focus it. The table moves. The Doctor tells them that what he is about to do, he learned from a mystic on Quantox (an ancient time mystic in the Qualactin Zones). The mystic made it seem very, very easy. The Doctor walks into the unstable area and vanishes. Clare gasps and lets go of the switch. Romana yells at her to hold it down. Clare obeys.

The Doctor appears between the College and his own TARDIS. In pain, the Doctor swims up the tunnel. Romana calls K9 to wake up and come to the console. He detects a circuit malfunction. The Doctor gets to the TARDIS and gets his arm through it but cannot get further. He starts to slide backwards.

K9 tells Romana that they can merely slow down deterioration of the circuits but not stop it. Clare's switch is getting very hot. Romana tells her to hold it down with a pencil. When Clare tells Romana she hasn't got one, Romana reaches for the table, for she cannot leave her switch either. Romana cannot reach it. Clare tells her she can and lets go of her switch. The console lets out a small blast and another blast occurs where K9 was plugged in. They are all thrown about.

In the vortex, the College Rooms and the Doctor's TARDIS are spinning wildly away from each other. The Vortex changes colour and the Doctor slowly vanishes.

Skagra fights with the controls to regain the equilibrium of the TARDIS and with help from Chris and the prisoners, he is able to stabilize the time machine. Skagra smiles. After he does, the prisoners and Chris also smile.

Romana bandages Clare's hand. They worry and wonder about the Doctor. Romana tells her they have to ahead with the plan as planned.

The Doctor finds himself regaining consciousness in a small equipment room in the TARDIS, which arrives in the Carrier Craft. Rummaging around the equipment on shelves, drawers, cabinets, and other spots, he finds the many pieces of what he is looking for. He puts it together but the last piece falls apart in his hands. As Skagra plans an infinite concert of the mind, the Doctor constructs a metal helmet. The Doctor tries to use the sonic screwdriver to fix the last bit that wouldn't work. The screwdriver does nothing at all. When the Doctor tosses the piece onto the table, the device beeps. When he picks it up, the device doesn't beep. The missing bit is Zinc and Lead Oxide which is contained in the paint on the table. Finding a small laser gun, the Doctor fires on the table.

K9 reports repairs completed. Romana calls him a good boy. She dreads to think what they are walking into. She hits controls along with Clare.

The Doctor thinks the aesthetic nature of the helmet device leaves a lot to be desired. A bit of table top is stuck onto the top of the helmet device. The Doctor starts out and finds the TARDIS main control.

Skagra and his Krargs and prisoners are in the Carrier now and the Krarg commander reports the fleet of ships are ready. Skagra sees the Wooden Door of the Professor's TARDIS appear and thinks the Doctor is in it. "Doctor?! That man is like an itching flea on my skin." The Doctor watches Skagra from the viewscreen, "Let's go and say hello." K9 emerges from the College Doors TARDIS. "He send his dog out to stop me!" Skagra mocks. He is stunned when the Doctor comes out of the TARDIS but tells the Doctor there is no room for him in his universe. The Doctor uses the helmet to control the prisoners against Skagra but Skagra turns them back to him. The Doctor tells him he has used his derenged billard ball once too often. When Skagra uses a Krarg on the Doctor, the Doctor orders K9 to stop it. K9 holds it off. The prisoners and Chris split into two groups, one for the Doctor and the other group for Skagra. The two groups start to wrestle. The Doctor skilfully edges Skagra toward the overheated Krarg, which eventually falls into the generation chamber and the vat inside. It begins to dissolve. More Krarg appear and K9 is hard pressed to hold them back.

Romana comes out of the Wooden Door and tips over all the vats of gas in the generation chamber. She also rips out main feedpipe. She also finds wiring and pulls out a bunch, hauling the wires back into the fray.

Skagra now has the Doctor backing away into the heated and burning Krarg group.

Romana calls Clare out and gives her instructions and a bunch of wire leads. The two females head for two ends of the room, opposite ends. Green gas fills the floor so the two girls put their wires into the gas and sparks fly across the room. The Krargs being to dissolve. This distracts Skagra and gives the Doctor the chance to send all the prisoners toward him. "Want to call half time, Skagra? We can have a short break if you like, few slices of lemon, gets you up no end!" Skagra flees to his Ship and orders it to take off. A block of light surrounds him and he vanishes.

Skagra appears in the white, red, and silver cell. He orders the Ship to let him out, calling himself the lord of the Ship. The computer voice tells him that her lord is the Doctor now. The Doctor is a wonderful, wonderful man. He has done the most marvellous things with her circuitry. She will tell him all about the Doctor. Skagra sinks to the floor, yelling for her to let him out.

Romana finds the prisoners are not seriously hurt, just in shock. Clare finds the same about Chris. The Doctor has dissected a few spheres. He will be able to unscramble all of the minds but it will take a few hours. Romana questions about returning the prisoners to Shada, a forgotten prison planet. The Doctor refuses to play judge and jury and takes the prisoners back to Shada and let the Time Lords take care of it. Salyavin made the Time Lords forget. He didn't want his escape to be found out.

St Cedds College: Porter Wilkins has reported to the police officer about the missing rooms. There is no black market for rooms, who would want a room. People take things from rooms but not the rooms themselves. Wilkins calls him sarcastic. He explains when he opened the door there was nothing but a blue haze. The policeman tells him the blue haze might be the vital clue they are searching for. Wilkins tells him he wasn't drinking. The policeman knocks and the Doctor calls for them to come in. Whoever took the room seems to have brought it back. The Doctor is reading to Chronotis, Clare, Chris and Romana. The policeman reports that this room has been stolen. Chris reports a bad headache. Hijinks going on last night. The Doctor claims the TARDIS is his. The Doctor takes his leave, telling the Professor they will keep his secret, and saying goodbye to all. Romana says goodbye also. The Doctor and Romana leave in the TARDIS which vanishes. When the officer sees the Police Box gone, Chronotis asks if he wants a cup of tea and asks, "What Police Box, officer?" The officer tells them to get their coats: they are to come with him to the bridewell -- the police station.