In the British Channel, a ship is being attacked. A Mayday says the ship is being abandoned. A grotesque hand cuts the radio operator off and he screams at something coming toward him.

The Doctor and Jo head via small engine boat to the Master's prison -- a large old prison on an island set off the mainland. The main gate announces them to the warden Colonel George Trenchard, who tells them ships vanish without a trace all the time. The warden checks their passes. Trenchard seems to be taking his time, causing the Doctor to quip, "I suppose we can always come back later," and "if we get the opportunity" to see the Master. The Master has not tried to escape which makes Jo and the Doctor suspicious. Trenchard wants to prove his men are immune to hypnotism. He sends a new man, Wilson, in to see the Master. Trenchard puts on a screen that shows them the Master's cell. "My word, he's putting on weight." Wilson thought the Master wanted his book changed. Jo, The Doctor, and Trenchard watch as the Master tries to hypnotise Wilson, "I am the Master and you will obey me." He fails and Wilson leaves the cell. Trenchard takes the pair to see the Master, who seems to be exercising on a rowing machine. The Master seems pleased to see the pair. Trenchard leaves; the Master tells them the "decent sort" Colonel used to be the colony of a small place -- the Doctor jokes that he thought it was of a very small colony that claimed independence soon after he arrived in England. The Master makes note that he has everything except his freedom. The Doctor tells him that many people were in favour of executing him. The Master claims that he has had a chance to think about things, he doesn't like being locked up, but he claims to be a changed man. He has a great deal of which to repent. The Doctor asks where he is TARDIS is so that he can make sure the Master cannot escape from this planet. The Master won't tell him -- that is too much. The Doctor asks if there is anything he can do for him. The Master wants the Doctor to come in and chat with him. As they leave, he says goodbye to Miss Grant and moves to shake hands with the Doctor but the Doctor raises his hand to wave. The Master chuckles. He told the Doctor he sincerely hopes they will meet again. After they leave, the Master laughs out loud as he starts rowing.

Jo asks the Doctor if he felt sorry for him. The Doctor claims "he used to be a friend of mine once... a very good friend... in fact you might almost say we were were at school together..." Trenchard stamps their passes again. The Doctor tells him that the Master is a very dangerous man. Trenchard gets one of his chaps to run the pair down to the keyside. They look back on the prison.

Trenchard is in league with the Master, who tells him not to underestimate the Doctor, whom the Master thinks is here to find the missing ships. The Master gets almost upset when he finds out Trenchard mentioned the ships vanishing to the Doctor. The Master asks him if he can get another TV, colour, one for the bedroom.

As they walk on the dock, the boatsman--named Thomas Robbins -- tells the Doctor he was part of a rescue ship that looked for survivors from the three missing ships, "Something queer's going on." A secret Naval research establishment is trying to hush it up. They found one lifeboat, the bottom all charred, and it was overturned. The Navy took the lifeboat and told the team to keep their mouths shut. The man will not take the Doctor to the Naval Base. The Doctor asks the man to look after his young friend... she was looking for some picture post cards to buy. He hands the man some money, telling the man to look for her since he cannot -- a bad leg from the Crimea, Gallopoli, and some other place -- lies of course -- he wants the man to move off so he can take the engine boat out himself. The man knows he is going to do this, of course.

HMS Seaspite Base: Captain Hart dictates to his secretary, 3rd officer Jane Blythe, a letter about transferring the life boat remains to HMS Vern in Portsmouth. Outside, Hart and the woman see the Doctor arriving on the beach. Hart calls the Master at Arms to report this stray civilian. The Doctor goes to the lifeboat as reported by the secretary. Soldiers come running but he says, "Good afternoon."

Jo pays the boatsman for his helmet and motorcycle in order to go look for the Doctor.

In his cell on a screen, the Master watches and whistles to the Clangers, clay mation TV show. "It seems to be an interesting extraterrestrial life form." Trenchard explains it is just a TV show for children. Puppets are on it. Trenchard has returned to bring him some maps to plan their next move. The Master tells Trenchard that Trenchard is wasted at this job. They find an abandoned sea fort in the centre of a triangle of the three sinkings. The fort is no longer abandoned as Trenchard tells the Master: it is being used as a solar testing station.

At this station, two men play cards; a heavy set man and a skinny man. Alan Clark, the heavy set man, wins a couple of quid. The skinny man feels funny about this place -- it's deserted and the two men are on maintenance, the only ones here. The skinny man feels they are being watched. A strange creature's hand rises up to the outer platform.

Hart questions the Doctor, who dropped in on impulse. The scorch marks are linear in nature. The Doctor tells Hart he never carries his UNIT pass, to ask Miss Grant for them. The Doctor figures that a concentrated beam of heat sunk the boat to make sure there are no survivors. A call comes to the secretary: Jo has arrived with two UNIT passes.

On the Fort, the skinny man hears a noise and takes out a flare gun for a distress signal if he needs it. He goes up to check out the sound. The heavy set man hears Hickman scream and a strange sound. He finds the man dead, his eyes still open. The man sees a strange headed monster being in some sort of string vest.

Hart wants Jo and the Doctor to go. He has no official power to allow them to visit the Fort. The Doctor tells Hart that Horatio Nelson wouldn't have waited for official clearance and adds that he knew Nelson as a personal friend, not from history books. Jo and the Doctor leave. Hart says, "Good grief, the chap's as mad as a hatter."

Jo and the Doctor arrive at the fort and climb the ladder up to it. Once inside, the descend steps.

Outside, a green hand comes over the side of their launch boat.

Alan, the heavy set man, is the figure and the Doctor uses his Venusian karate to stop his attack. The man rants about sea monsters. Sea Devils he calls them. One of the monsters is watching them get him to a bed. Alan points out the radio... the things ripped it out and took it away. When the Doctor asks about a transistor, Jo asks him "What do you want to do, listen to NIGHT RIDE?" The Doctor can turn the receiver to an output radio and explains how to do it -- modulating the signal, connect the output of the loudspeaker into the input of your low frequency amplifier, then connect the low frequency putput into your oscillator and use the loudspeaker as a microphone. The transistor radios are in the crew's quarters. The Doctor gives the man a shot to calm him down and then leaves to get the transistor radios. The Doctor comes face to face with a Sea Devil and tries to communicate with it but it shoots a strange sucker like gun at him, causing a flare up in the wall behind the Doctor. The Doctor leads it on a chase but runs back to the room that Jo and Alan are in. He barricades the door -- reptiles like "those creatures in the caves" and completely hostile. The Doctor works quick as the thing starts to heat ray through the metal door. It reaches in but the Doctor uses his make shift hook up to electrocute its arm. The Sea Devil runs away in pain. The Doctor and Jo follow it but it seems to have jumped out a high windo.

Hart returns to his office in the morning. Jo and the Doctor have vanished, Jane tells Hart. She also cannot raise the Fort. Hart calls Air Sea Rescue.

The Doctor has made his radio device. Jo comments she's seen things like that in a Modern Art Exhibit. The Doctor picks up Jo's favourite DJ -- who tells his audience that he is playing to all, whoever they might be, isolated wherever they are. The Doctor thinks he got his wires crossed somewhere. Jo asks, as she puts the blanket up on the sleeping Alan's body some more, about the mention he made of having seen these creatures before. He explains about the Silurians -- who appeared in Derbyshire. The Doctor tells Jo that the man who discovered the Silurians misnamed them... they should have been called Eocenes. Jo wonders what the humans have done to them "as far as they are concerned, man is just an ape who got above himself." The Doctor sends out his Mayday. As Jo doubts he will get an answer, someone calls and is about to land. A helicopter lands. The Doctor tells himself his radio set up was a remarkable piece of work -- just seconds before the box sparks and smokes up in his hands. He drops it.

Trenchard sent a man to the mainland to get some gear for the Master -- a sailor captain's hat for one thing. The two are planning to leave the prison.

The Naval Base: Hart wants proof about the ridiculous story about Sea Devils. Jane calls Sickbay to check on Alan but he is still delirious and babbling something about Sea Devils.

A man drives Trenchard in an open car-van to a brick building -- the Naval base -- where Trenchard tells the driver to go to the Petty Officer's Mess. When the driver leaves, Trenchard knocks on the side of the car and the Master comes out from under a blanket in uniform. He salutes as men pass in marching.

The Doctor wants to contact the Sea Devils to find a peaceful solution. Trenchard comes up to Hart's office. He holds Jo's hand and says hello, asking Hart about golf and the weekend. The Doctor wants the Colonel to leave so he can get on with the Sea Devil business. Trenchard says something that makes Jo and the Doctor realize he is in league with the Master.

The Master is in a storeroom where he finds some equipment. A chief, CPO Smedley, enters and asks about him. Special Audit Officer from Civil Defense is what the Master claims to be -- the items in his bag are defective. The Master tries to hypnotize him into thinking he has seen his pass already but when the man fights the hypnosis, the Master hits from behind with a chop. The man falls.

Hart finally gets George Trenchard out of his office. When Trenchard pushes off, Jo will not shake his hand nor let him hold it. When he leaves, the Doctor tells Hart ships must be kept away from the shipping lanes, despite the complaints that may come. Jo looks out the window and sees the Master. She tells the Doctor but the Master moves on. The Doctor believes her and tells Hart to issue a full security alert. Jane tells them someone has been found unconscious in the electronics solar storeroom. Smedley explains about the Master attacking him. "Who is the Master?" Hart asks. The Doctor fingers Trenchard as the Master's helper. Jo returns to the prison with the Doctor where Trenchard is in his office "in conference" he says as the knock on the door from the Doctor comes. The Doctor barges in and tells him the Master has escaped. Trenchard shows them the TV scanner where the Master sits in his cell. Trenchard will go and check the guards himself. Jo checks the hallway so the Doctor can call an outside line but he finds he cannot -- the phone's outside lines are both dead. He tells Jo to take the jeep to call UNIT from a Naval base phone and tell them that Col. Trenchard and his entire staff are to be replaced. Jo worries about the Doctor but leaves at the Doctor's urging.

Trenchard tells the Master that the Doctor knows. The Master tells Trenchard to get the Doctor down to his cell -- to see him alone. He lies, telling Trenchard that he can convince the Doctor to see things his way and to keep quiet. The Master, after Trenchard leaves, does something to the TV camera that is watching him in the cell. He rings a bell for the guard and tells him the air conditioning vent is blocked -- something seems wrong with the air flow. The Master hits the guard and takes his knife.

When Trenchard returns to his office, the Doctor hits a hole in one into a bottle using the golf ball and club--and blindfolded. Trenchard tells the Doctor to go see the Master himself and when the Doctor leaves, Trenchard calls his men to stop Miss Grant, "She is not to leave."

Trenchard and a guard return to the Master's cell and Trenchard's voice causes the Doctor to turn his head around -- and the knife just misses it, implanting itself into the wall close to his head instead. The Master concocts some story that the Doctor was here to kill him... the Doctor thinks only a fool would believe something like that... "Though I suppose in your case..." The Doctor is put under arrest. After the Doctor leaves, Trenchard voices that it is all getting out of hand.

When they won't allow her to use the jeep and tell her that Trenchard wants her returned, Jo uses self defense against the two guards and gets away.

The Doctor questions the guard who is with him in Trenchard's office. The guard seems not to hear. Trenchard returns and tells the Doctor that he is a prisoner and that he believes his UNIT pass is a fake. The guard takes the Doctor away. Jo hides as dozens of guards search for her.

Trenchard returns to the Master as the Master is working on some device. Trenchard tells him that Jo Grant is on the grounds but the guards should pick her up at any moment. The Master wants the Doctor sent to him.

Naval base: Hart talks to Robin Ridgeway, a Naval lieutenant commander of a sub. 70 ships have vanished before but not so many so soon. Ridgeway will search for the cause.

The Doctor is brought to the Master and they talk, the guard taking off the Doctor's handcuffs. "How very kind of you," the Doctor says but the guard ties the Doctor's hands and arms behind his back in the chair, "How very unkind of you." The Doctor and the Master are left alone to verbally spar. The Doctor stalls that UNIT knows it all. The Master knows about the Sea Devils from stolen Time Lord files and wants to contact them to make them the rulers of Earth once again.

Ridgeway's sub starts out, contacting Hart and a radio operator.

Jane is worried about Miss Grant and the Doctor, lets Hart know about this, and suspects Trenchard is up to something.

Ridgeway brings the sub up to a level where he can look out the scope.

The Master will take pleasure in seeing the human race, which the Doctor is so fond of, being destroyed. Trenchard demands to see the Master.

Jo hides at a gunnery testing block outside as a jeep of men pass.

John Hart's guard is coming to the main gate with Hart.

Jo sneaks around the outside of the castle-prison and finds a window where the Doctor is hidden. She gives him some message using her hands, facial expressions and fingers, then she sneaks to another window and goes into it, finding herself in a hallway alcove. She hides from a soldier snooping around. The Doctor checks the time and yells at the guard, wanting to talk to him. The Doctor asks about the Geneva Convention -- how long is he to be kept here like this. Jo sneaks in and hides behind the door, readying her pocket book as a weapon. The guard leaves though so Jo uses a compass to undo the Doctor's bonds.

Trenchard explains himself to Hart, who wants to see the Master. Trenchard shows the Master to Hart via the view screen. Trenchard calls the Doctor a cranky fellow. John Hart leaves.

The sub is under the surface and receives a contact. Sonar goes crazy but the lights go out and the power seems to go dead. The sub seems dead in the water.

The Master thinks Trenchard handled Hart well. The Master has made a replica of a communications device used by enemy agents. The Master claims he will use it to lure the most dangerous saboteurs out of hiding and into a trap. Trenchard will expose the criminals -- all a story told by the Master. Trenchard tells the Master he doesn't want any reward--he was just doing his duty. The girl has not been caught yet. A guard is to take the Master back.

Jo undoes the Doctor, who gets the guard back in to the cell. There, Jo bends down behind him so the Doctor can head butt him over her. The man tries to get up but Jo chops him in the chest and he stays down. The Doctor keeps saying, "After you..." to Jo who said, "After you..." "No, no, after you," the Doctor said.

Back at the Naval Base, Hart tells Jane to get on to UNIT and see if there is any news of the Doctor and Miss Grant.

Hart's man Ldg Seaman Lovell tracks the submarine. The sub is drawn to the bottom of the channel. Lt Commander Tony Mitchell, the second, reports there is nothing wrong with the ship but nothing is working! They hear banging on the outside of the sub -- it cannot be divers. Forward section is being attacked and something is coming in through the escape compartments. The commander hears men on the mike screaming.

Trenchard wants every available man to find the Doctor and Jo -- two dangerous enemy agents. Sector 27 is where the pair are headed now: toward the beach and a mine field. A man calls in after spotting them. The Master says they are trying to rejoin their associates at sea. The Master turns on his device which whines loudly.

The Master tells Trenchard about the Sea Devils. The Doctor and Jo flee through the minefield. The Sea Devil shoots two of the men at the jeep down. Jo and the Doctor pass barb wire, the Doctor laying down and Jo walking over him; the Doctor flips himself over it. He uses his sonic screwdriver as mine detector. The Master wants the beast to attack Jo and the Doctor. The Doctor uses the sonic screwdriver to set off the mines to draw the Sea Devil away from the minefield, it screaming. After it goes back to the water, the Doctor and Jo make their way across the mines.

Hart knows something is wrong with the sub and sets up a full scale search. Ridgeway tells Summers, a diver who is going to try to make his way to the surface, to alert Hart. Another crewman Johnson goes to another door with an auto weapon. The things are burning their way through the hatch doors. They melt their way in. A Sea Devil comes in and looks around.

The Master tells Trenchard to be calm and finally tells him the whole truth. Yet he delays Trenchard's telling of the Sea Devil plan to the authorities. Jo is hidden near a large bush tree by the Doctor until the men in jeeps from the prison pass by. The Master tells Trenchard not to allow Hart to check on the prison, "I assure you all your troubles will soon be over."

The Sea Devil on the Submarine seems to be cooperating with the men on the sub, directing them to their base. Hart doesn't believe a word of the Doctor and Jo, who have walked ten miles across open countryside. Jo says, "The Doctor's seen these creatures before." "Oh, I'm sure he has, Miss Grant," Hart says. The Doctor takes the explanations and also Jo's food which Jane brings to her, "For Heaven's sakes Jo, what do you think this is, a picnic!" He eats the food and offers some to Hart and Jane. Jo asks for some and he says, "So sorry," but hands back the plate to Jo, who finds nothing. Jane will get some more. No sign of the sub -- it's missing too. Hart asks what the Doctor wants him to do. The sonar man gets something -- the sub -- heading for the beach by the castle.

The Master gets some communications. Trenchard wants to give the authorities some notice about these creatures. The Master doesn't want to be interrupted. Sea Devils rise out of the water and head up the beach toward the castle. Dozens arise. Trenchard calls the Minister but cannot reach anyone important yet. Sea Devils enter and kill guards including Drew and Barclay. Trenchard watches the Master work on the device and calls for a guard but the guard is being killed by a Sea Devil who comes up the steps. Trenchard opens a desk drawer and takes out a pistol. Two guards see two Sea Devils and one rings out an alarm. The solar guns used by the Sea Devils kill two more men; most of the lads are dead already. Trenchard tells a guard to use a phone in his office -- a direct line to White Hall. Trenchard shoots his gun at a Sea Devil and gets one. Sea Devils come in to the Master's cell... a dead Trenchard lying in the hallway.

Hart's contact of the sub fades. Hart sends a team of armed men in two land rovers to the main gate of the castle. Jo and the Doctor join them. They find dead men and then Trenchard. "The Master had no further use for him," the Doctor said. The Master used Trenchard's patriotism against Trenchard himself as a weapon.

Jo returns to Hart, "He's gone." The Doctor is taken down to the Sea Devils' underwater base in a strange cylinder with wires running from it. Parliamentary Private Secretary Robert Walker comes in to Jane Blythe and asks for breakfast!. He also meets Radio Chief Bowman. He hands Jane his jacket, hat, and umbrella. Walker has come down to clear up the ship vanishings -- the Minister has put him in full charge.

The Doctor verbally spars with the Sea Devil leader, telling them his people abandoned Earth to its fate and that he has met his kind before. The Doctor tells them they will be bound to lose. There are other colonies all around the world in hibernation. "Why can't you share the planet!" The Doctor thinks there would be a chance man would agree to the Sea Devils living in the deepest depths of the ocean. The leader will consider it -- perhaps it will be possible. "NO! The Doctor is your deadly enemy -- he must be destroyed!" The Master has arrived.

The idiot Walker thinks they should attack. Hart protests that some of the men that are captured may still be alive and Jo feels the Doctor is also. Walker has looked up the UNIT file on the cave creatures that the Doctor encountered before -- the Brigadier blew them up. Walker agrees that war is murder--then wonders where that girl is with his toast. Walker has already given the orders for ships to converge from all over. Navy ships -- a task force -- will be in position soon.

The Doctor begs the Sea Devils not to listen to this "personification of evil" who wants only to provoke a war. The hibernation unit is faulty and they need the Master to repair it. The Master explains about the last time the Doctor encountered their race -- the humans destroyed the creatures. "I tried to make peace but I failed," the Doctor admits. The Master says man is weak, The Doctor says man is strong. The leader touches the Doctor's head and does not think he lies. He thinks it would be better to make peace and the leader will consider what he has to say. The Doctor puts his hand up and the Sea Devil puts his hand up to the Doctor's.

But the Task Force has arrived and send down depth charges. They inform Hart and Walker. Walker says, "Cry let slip the dogs of war!" Jo tries to get Hart to stop Walker but Walker threatens to replace Hart. Hart says, "I'm sorry, Jo." He gives the order.

The Doctor is about to make a truce with the Sea Devils -- as a gesture of good faith, the Sea Devils will release the captured sub and men. The Master argues that they are throwing away control of this planet. To assure he is right, the blasts from the humans' ships shake the undersea base. The Sea Devil feels the Master is right and orders the Doctor taken away and killed The blasts allow the Doctor to get free and rubble buries the two Sea Devils that were holding him. The Doctor takes the rubble off of one and finds the heat ray gun at the belt. The Master tells the leader to send the Sea Devil people to the lower levels and convince the humans that the attack has been a success. Sea Devil bodies come up from below and the Task Force finds them... the lizard things. Hart wants the attack called off. Walker isn't sure he should but Jo and Hart plead with him to abandon attack.

The Sea Devil control room opens a screen to view the ships of the humans getting out of range. The Master convinces the leader to let the ships go -- let the humans think they have won. The Master touches hands with the Sea Devil. The Master wants to attack the humans' base to get electronic equipment to build a new trigger mechanism for the hibernation reactivation units -- the old one is faulty.

Number One man of the Sub is trying to open their cell door. Ridgeway admires his pluck and gives it a go, not expecting it to work. The Doctor's face appears at the porthole, asking if they would mind standing back. They do and he fires the ray on the door, freeing them. The sub is in working order except for the radio and the escape gear. It is in an undersea harbour. The Doctor gives the Commander the ray gun.

On the sub, two crewmen play cards and lose to an officer named Summers. A Sea Devil watches over them. The officer says a noise is loose rigging but it sounds like SOS. He writes a note on the paper to play Consequences. The older crewman fakes he is sick. This distracts the Sea Devil who wins the fight but the Doctor and Ridgeway return, coming down the ladder into the control room. The Doctor doesn't want it killed but Ridgeway does kill it with the ray gun, "No! don't kill it! There was no need to have done that." The Sea Devils find out the humans have escaped. They activate a forcefield around the sub and this stops the sub. The Doctor thinks they could try firing the torpedoes at the cave wall but that will risk blowing themselves up. The forcefield increases and the sub loses some power. The Doctor tells Ridgeway he has to risk it. He orders the torpedoes fired and this shakes the sub about but causes no damage. The sub is free and is about to surface. Ridgeway says, "We're going home."

The Master tells the Sea Devils that before the humans can attack the Sea Devil base, the Sea Devils will attack the humans.

The Doctor disarms the Sea Devil but more arrive and has to use his Venusian karate on them. But one gets behind him and forces him down from his shoulders. The Master stops the Sea Devils from killing the Doctor, Jo and Hart and allows them to take the Doctor inside with Jo and Hart helping the Doctor up. The Master nods, "Dear oh dear, Doctor, will you never learn." Hart and his men are soon put into a warehouse. The Master tells a recovered Doctor that this is the first step to returning the world to its rightful owners. There are bases underground and underwater -- with the Doctor's help he will revive them all. He tells the Doctor to cooperate if he values the lives of every man on the base.

Jo, Walker and Hart are in an office with the radio. Walker is afraid -- asking if they should leave things to the Doctor -- he made them a promise, Walker afraid of reprisals against the innocent.

The Master wants to build a signal trigger mechanism sonar device similar to a laser to revive every other base in the world of the reptiles. The Doctor thinks it is possible. "Good grief, what on Earth do you think you're doing?" There are circuits misplaced. The Doctor sees more power is needed through to the main dipode.

Walker wonders if a mere child (Jo) should risk her life. Jo gets through the shaft which goes onto the roof of the building. Neither Hart nor Walker could fit. Jo crawls to the vent and gets out onto the roof. A Sea Devil almost sees her as she climbs down a ladder and runs around the building to look into a window where the Doctor is working. He needs a polarizing condenser. The Master leaves and Jo opens the window, "C'mon Doctor, hurry." The Doctor has other plans. He will create a distraction and he wants to free Hart and the other officers. Jo rounds a corner but runs as two Sea Devils come marching. They don't see her. A Sea Devil guard comes in to the Master and the Doctor when the Doctor tests his device and the sound makes the Sea Devil hold its head. Jo gets the door open for Hart and Walker. She and Hart run out as the Sea Devils are in pain. Hart gets a rifle from one of the dead men and fires at some chasing Sea Devils. He and Jo get to a hovercraft and escape. The Master switches the power off and asks what happened. The Doctor feigns that he had the frequency too hard. He had the output in the input socket. He fixes it. The Master doesn't want the Doctor killed now -- he might prove useful. The Doctor is to come with the Master. Outside, the party see a returning hovercraft with Hart and troops. The men storm the base and start firing at Sea Devils. A Sea Devil shoots a man down. Jo is out of the hovercraft last. From a roof, a Sea Devil shoots a man but another man shoots that Sea Devil. A soldier comes in and shoots a Sea Devil in front of the Master, who was put behind the Sea Devil. This officer is left with the Master, who hypnotises him into sleepiness, then hits him down. Hart gets behind a cannon device turret and starts firing at Sea Devils. The Doctor asks where Jo Grant is: the beach. The Doctor spots the Master running with the device to a sea scooter which the Master steals and gets away in. The Doctor follows him in another. Surviving Sea Devils race into the water to get away. The Doctor follows the Master through choppy seas to a beach where a Sea Devil diving device is and many Sea Devils arrive. "I'm sorry, Doctor," The Master points to the creatures and laughs

Walker will request a massive nuclear strike despite Jane explaining that Lt. Scott has reported the Doctor is out to sea. They figure, despite Walker at first thinking the Doctor has gone over to the other side that the Doctor was after the Master.

The Sea Devil leader hears the debate between the Doctor and the Master again. The leader is not willing to listen or reconsider war. Too many of his people have died. He will destroy the humans and reclaim the planet. The Doctor tells him the power will take time to build up. The Master suggests they dispose of the Doctor. The leader orders the Master and the Doctor taken to cages. As they are taken, the Doctor says, "You seem to be losing your touch." In the cage, the Doctor gloats a bit and tells the Master, "I reversed the polarity of the neutron flow." This means there will be a massive reverse feedback in the Sea Devil power system. A massive explosion. No one can hear the Master call for help. The Doctor built a self destruct system into the main control switch and it cannot be turned off.

Walker contemplates his victory, "Now how bout some tea." Jo starts to cringe and cry.

The Doctor uses his sonic screwdriver, "You see, come on." They have the diving suits from the sub which escaped. The Doctor gives the Master one. They will find the airlock to get down to the capsules.

Walker gets smoked salmon from Jane. Hart goes to the radio room where Jo and Bowman are. Hart orders a high speed boat to make a complete sweep of the area before the attack. Bowman sets it up. The hovercraft picks up the Doctor and the Master. The hibernation device causes an overload of power. In the hovercraft the Master holds his chest and falls. The blast rips up from the sea. Bowman reports about the two survivors, one of them in a bad way. Jo wonders which one.

The hovercraft returns to the beach. The Doctor comes out to Jo. The base is destroyed. The Doctor did what he had to prevent a war. The Master is brought out on a stretcher -- dead. It was too late. An MD tells them a doctor in the hovercraft said it was too late. The Doctor pulls the Master face mask off the driver of the hovercraft... he is alive but hypnotised, "I must obey... I must obey... I must obey..."