Braun, a man with greying hair comes out of a cubicle of advanced design in a strange otherworldly jungle on the planet Zeta Minor. He plants a burial marker near many others: Egard Lumb died 7y2 in the year 37,166 (Morestran Year). Two men -- Professor Sorenson and Baldwin -- further out, near a black hole in the ground are taking specimen soil samples in Sector 5. Braun has taken a sun shot, the two men have 15 degrees until full night. The two men must leave now. The last time they hit a rich vein, Lorenzo died -- when all the deaths started. Sorenson tells Baldwin the planet is alive and watches every move they make. It hides the veins of minerals. Baldwin leaves Sorenson when the obsessed man will not leave. Braun takes a blaster rifle and exits the cubicle but a burning sound occurs and he yells, falls on his back, and slowly vanishes into nothingness. The jungle is alive with sounds of night creatures. Baldwin treks through misty growth and foggy water. He sees strange spiked plants but runs past trees, back to the cubicle base. Entering the base cubicle, he hears a burning sound. Before it attacks him fully, he hits an alarm -- a distress call. The sound grows closer and it makes him fall and a louder sound hits. He vanishes also, screaming.

In the TARDIS, Sarah watches the pensive Doctor, showing her watch and asking him how long they have been travelling. He promised her they would be back in London five minutes before leaving Loch Ness. They are on the edge of the time-space vortex. Sarah asks what has gone wrong this time -- he always gets rude when he is trying to cover up a mistake. They came out of the time vortex 30 thousand years too late. They hear a distress call. The Doctor, gets that obsessed look of his own, "Stand by for emergency materialization." The TARDIS appears and the two exit into a strange forest. The Doctor has a device to track the caller. The lines of interference from the time warp shrouded the call. Sarah suddenly gets mesmerized by the strange burning sound and stares at an invisible force.

A space ship approaches the planet Zeta Minor, the last planet of the known universe as older man, the experienced Vishinsky says, looking at a screen. Orbit entry is imminent. Cold Controller, the commander, Salamar does not want to scan before sending non landing party crewman Vishinsky down. Salamar claims Vishinsky is the most experienced. Professor Sorenson and his team of eight men have been on the planet for months. Salamar has no fuel for a low level scan--they have enough for return journey and an emergency reserve.

The Doctor notices Sarah's state and asks what is wrong. She does not know but only that she feels odd in her mind and her body. She seems all right now. The Doctor found a hand tool of some kind. Sarah feels this means the people who sent the signal must be human. Vishinsky, Ponti, De Haan, and two others will be sent down in the descent chamber as soon as the ship goes into orbit. Sarah and the Doctor find an almost skeletal body (Braun) which makes the Doctor think they are several months too late. The pair go into the cubicle and find the auto distress button. It may have been running for months. The Doctor thinks the base is geological scientific study, "A lost expedition." He will go back to the TARDIS for his spectromixer but Sarah figures she can do that alone. That will allow him to pinpoint their position by a star above. He will work to restore power. The Doctor gives Sarah the key to the TARDIS and she leaves.

Opening a door, the Doctor finds the body of Baldwin and worries about Sarah, who returns to the TARDIS, wary. A bush moves. The rescue team see the TARDIS and report that it is hostile and alien. They apply a device to transport the TARDIS to the ship's quarantine berth. This device also does not allow Sarah to open the doors. Sorenson comes out to Vishinsky and his men, having observed them for some time -- for this planet can be deceptive. It is nearly dawn and the days are safe. Sorensen tells him the mission is a success. He leads them to the cubicle base where they find the Doctor over the dead body of Baldwin and power controls. The team point blaster rifles at the Doctor.

Sarah opens the TARDIS doors finally and goes out to the Controller Salamar. She finds it hard to breath---so he orders a man to transfer oxygen to the quarantine area. Vishinsky reports the Doctor to the Controller. The Doctor interrupts by suggesting his receivers might be better than their's -- to which Ponti hits him lightly and tells him to shut up. The Doctor says, "My manners certainly are." Sorenson is in shock and in a strange mental state.

Sarah is brought to Salamar.

A strange sound, as if a monster is alive, is near the hole.

Sarah tries to talk to Salamar, who tells her that Zeta Minor is beyond Cygnus A, as distant from the Artoro galaxy as that from the Anterides. She tells him they came from Earth but she doesn't get anywhere trying to explain to Salamar -- she comes from Earth, but the Doctor doesn't. He has her taken away.

Salamar orders a landing and the ship follows the team down, lowering the ladder ramp to a high platform which one has to climb down. Several men do and move out into the forest with rifles.

Sorenson tells them about the men who died: Lorenzo, Duru and Somers. Then for a bit it stopped. Salamar wants the Doctor to confess to spare himself interrogation. Vishinsky tells Salamar that they cannot contact the Home Planet this far out. Salamar orders his men to prepare to execute the two prisoners.

The monster is shot at by O'Hara, the guard. This gives the Doctor and Sarah time to retreat but the thing burns O'Hara into dehydration -- first he vanishes, then his body is a dried up husk. De Haan and Ponti heard his scream. Sarah and the Doctor find O'Hara's body while Salamar and Vishinsky try to figure the power loss that just occurred. The Doctor has a very unpleasant theory about what the monster was. Ponti reports to Controller and Vishinsky. They check the cubicle cell and find the two missing. Alarms ring out and Ponti, De Haan, and the other men start firing at the fleeing Doctor and Sarah. Ponti returns and claims the aliens killed O'Hara. He takes them to his body. Salamar wants them recaptured and made to pay for this. Sorenson is under medicare in the Probe Ship. The Doctor gets hung up in a vine but he and Sarah take cover as a wind-like force with the burning sound passes. As night burns out, the thing leaves. The Doctor quotes Shakespeare, Romeo and Juliet: "Night's candles have burnt out and joggin day stands tiptoe on the mountain top or something like that." Sarah follows the Doctor into the jungle.

At dawn the occuloid tracker, a flying eye camera device is launched from the Probe Ship's side (projectile chamber three). It is in pursuit of the pair of fugitives. It sends back a constant picture to the ship's control room. The pair hide from the device which Sarah wonders if it is an elfin spirit of the forest. The Doctor tells Sarah he met Shakespeare once, "Charming fellow, dreadful actor." Sarah suggest that is perhaps why he took up writing.

Sorenson tells Salamar the dead men died of total dehydration. There are no external injuries. Rapid freeze drying. Sorenson feels it is irrelevant -- he came to the planet to save their civilization. Their solar system is dependent on a dying sun; rock formations here on the fringe of the universe may be an new source of power. He demands his mineral samples be loaded on board. Salamar is aware of Sorenson's high position on the Science Council but this is a military force and the manual says that hostile alien forces must be sought out and liquidated.

The Doctor and Sarah find the black hole. The thing does not live here... or anywhere. It just is. The Occuloid tracker finds the pair. In the dark pool there is no reflection. The men from the Probe find them and search them roughly. The Doctor wants to empty his own pockets but Ponti yells that he wants the Doctor's hands up. "I've nothing up my sleeve if that's what you mean." Ponti gets a pain and falls backward as he tries to search Sarah. Sarah reaches out and almost saves him but he falls into the pool, yelling. The Doctor yells at the men, "Get back!!!! Haven't you learned anything. You're tampering with the balance of nature on this planet in ways that you don't understand!"

Sorenson wants De Haan to load his canisters. 6 pounds of this mineral will produce enough heat equivalent to the output of their own sun over three centuries. Full scale exploitation of this planet will provide perpetual energy whenever they need it. De Haana doesn't fully understand the implications. He is taking canisters from the base.

Vishinsky and Salamar wonder how the aliens killed seven men. The former tells the later that he should not antagonize Sorenson. The professor has contacts in high places and authority in high circles. The Doctor and Sarah are brought in. They claim not guilty. Salamar does not want the Doctor to respond to questions with questions. They will be silent and failure to comply will result in their execution. A frightened look from Sarah shuts the Doctor up. When the time comes, he has to explain that there are boundaries here on Zeta Minor between existence as they know it and the other universe... each the anti thesis of the other. Sometimes called nothing... word to cover ignorance. Centuries ago, scientists have called it anti matter. They have existed side by side since the beginning of time. The Doctor tells an approaching Sorenson that he cannot take any samples from this planet -- if the takes some, they will never leave this planet. Vishinsky seems to believe the Doctor. Salamar cares more about his being in command than about the situation.

The Doctor is tossed face first into the quarantine room and he falls on his face. Sarah follows, "Do you ever get tired of being pushed around?" The Doctor stands up and folds his scarf, "Frequently." Sarah mentions they could get in the TARDIS and disappear but while it is tempting to let them destroy themselves, it wouldn't be just them... it would be the end... catacylsm... the big bang... the end of the universe. They find rocks from around the pool in a can -- they change colours. The Doctor takes some and puts it in an old toffee tin from his pocket. Sarah asks what he is doing and he doesn't seem to notice right away but he tells her he is testing a theory.

As the Doctor predicted, psycho stimulators not responding, the ship cannot lift off. Sorenson alerts their attention to the window -- the monster attacks the ship, looming large. It is pure energy in physical form as Sorenson notes. The energy barrier won't work...there is not enough power so Salamar orders the men outside to stop it. He also has the Doctor and Sarah brought up to the control room. "You sent those men to their deaths," the Doctor says. A man dies, falling off the platform and another. The Doctor tells them to link the forcefield to the atomic accelerator. Salamar hesitates but at Vishinsky's urging, does order this. This repels the monster. The Doctor tries to appeal to the scientist in Sorenson. He warns about tampering with the forces. They must abandon the canisters. The Doctor tells them to find an alternative energy source, the minerals cannot replace the power they will lose from their dying sun. The Doctor is not entirely without influence -- so he can communicate the intention to leave empty handed. Salamar wants the girl to remain here. Sorenson starts out of the room with the Doctor but he sneers that he must go alone. Sarah says, "Doctor..." The Doctor turns, "Yes, I know -- I'll take care." He leaves the Probe and the Occuloid tracker follows him.

Salamar wants to eject the canisters but Sorenson tells him his mission is to get him and the positron materials back to the Home World. While the pair argue, with Salamar winning, Sarah slips out into the forest, toward the hole.

The Doctor plunges into the hole deeper and deeper, odd colours and twists of existence churning him round and round until it stabilizes. The monster is there, too. De Haan and Morelli take the canisters beyond the forcefield area from the ship's quarantine cell (near the TARDIS). Sorenson is following them. He hides under steps as De Haan complains about flying back and forth, and taking things inside and out again. Sorenson sneaks into the cell and takes one of the canisters to hide it in the ship.

Sarah calls for the Doctor by the hole when he climbs up. She helps him out and up. He talks gibberish, "Vandervelt's equation of knowledge -- it's quite wrong." He keeps passing out.

Salamar orders immediate take off but Vishinsky cancels the take off when he sees Sarah with the Doctor at the hole on the scanner screen. Salamar objects but allows Vishinsky to go out to help the pair.

Sorenson makes a taped report about the positron elements which have shown a rise in toxicity. As he talks, the crystals change colour in the open canister. He is in pain and his eyes glow with red energy. He sees this in the mirror and takes a drink of smoking liquid. His eyes return to normal.

The Doctor is taken to sickbay in the ship and his stretcher is attached to the wall as a table. Mental function is barely readable. Vishinsky orders more stimulation. He comes around. Sarah thanks Vishinsky.

Psycho stimulators are activated and the countdown starts. The Doctor wakes up and asks her what the noise is. He promised the canisters -- as a Time Lord he promised the canisters will be left behind. Sarah asks him if he entered another universe to have a chat with it. The alarms ring out and the Doctor realizes it is due to the sample of minerals in the Harrogate Toffee tin box he has in his pocket. It is how he survived the pool. Salamar calls the Doctor an idiot and orders Morelli to get it to the ejection hatch fast. In the hall, De Haan asks Morelli when they will get lights on down here when Morelli passes, gasps and dies. De Haan finds his dehydrated body. They will not have enough fuel to get back if they keep this up: not being able to get away from the planet; the Doctor telling them there must still be anti matter aboard. To make matters worse, Anti matter and matter can cause annihilation when they meet. De Haan tells them Morelli's dead, killed by an animal in Sector 3. Vishinsky restores all walkway lights and leaves, wanting De Haan to show him and others where.

Sorenson is the animal. He drinks a potion of his own making and holds his face, returning to his normal human face as he can see it in the mirror, some elements of the drink are wrong. A crewman calls to report to sector 3. He asks what for.

In sickbay, Vishinsky finds the bone marrow in the body dehydrated. The body pallet is sent out, making the body in the pallet go out of the ship into space. The forcefield was phased to cut in automatically when the Probe took off -- they wonder how the thing got on board.

In the hallway, Sorenson tells Salamar that alien technology might have caused the deaths, something Salamar doubts. Sorenson suggests that machine in the quarantine cell might have some answers.

In sickbay, Vishinsky asks what religion Morelli was: Morestran Orthrodox. As the body is sent out, Vishinsky plays music The Last Stripes. This is part of disposal procedure. Sarah calls this procedure horrible -- the good soldier drifting forever. The Doctor would like a medical check on everyone on ship, someone is contaminated. Salamar comes in with a raygun, blaming the Doctor. Sorenson suggests other civilizations are desperate to get their hands on the power source. The Doctor scoffs at Sorenson's theories, telling him he might be wrong about this anti quark theory. If the Doctor and Sarah will not cooperate, he will kill them without compunction. Reig calls that the ship has stopped moving, the progress register has stopped. Salamar takes the Doctor and men up to the control room. He leaves Sorenson with the girl -- Sarah. The Professor, who is holding his arm, asks what her friend's field of science is. "Awww, everything, he's brilliant!" Sorenson tells her the Doctor has to be wrong and he gets close to yelling. Sarah tells him they are not arguing. The Doctor tells them they have come to the end of their piece of elastic -- there is still some aboard... when they reach the surface of the planet then they will stop with a bang. Salamar is wrong again the Doctor says. He takes the Doctor out of the control room.

Sorenson is explaining to Sarah about antimatter when he covers his eyes and there is a burning sound. Sarah is once more mesmerized by the force but Sorenson leaves via an opening door. Sarah comes out of it.

In a hallway, Sorenson passes De Haan, who is checking the floor. Sorenson climbs the steps but goes back down them, now transformed into the anti monster. De Haan is killed and his screams bring Sarah running out of the Sickbay.

The Doctor tells Salamar, "Usually I only entertain friends in the TARDIS." He also tells him it resembles a London Police Box. Salamar wants him to open it but they hear Sarah's screams. The Doctor punches Salamar down and runs out to her. The thing is just finishing off De Haan as Sarah sees it leave when the Doctor calls. He figures it is a hybrid creature... anti man. Salamar blames them for killing De Haan and shoots the Doctor in the face. The Doctor falls. Vishinsky arrives and stops him. But Salamar orders them taken to the ejection chamber to be put onto pallets...

Sorenson drops some of his potion. But he drinks some and Sorenson's eyes have become red with active energy. He falls on his bed.

The fight stops when Reig on the command deck is attacked and killed. Vishinsky reverses the pallets, bringing the Doctor and Sarah back up. Vishinsky gives a red alert, taking over command from Salamar who tells him he will regret this. Sarah gets the Doctor up out of the pallet and tells him what has been happening. Sarah tells him it is the thing from the planet -- she felt the same sort of icy suction. They pinpoint Sorenson as the anti man--he's been effected by anti matter; his brain cells are being destroyed and he will descend to the level of a primitive. The Doctor sends Sarah to command centre to tell them to shut down all the hatches. He leaves without telling her what he will do.

Senior crew leader Rachett is in the Solarium Section. All are on full alert. Sarah arrives, telling them Sorenson is behind all this. Something on the planet effected him. Vishinsky believes it, "The Doctor has been right so far -- we should have listened to him before." The section hatchways close. The Doctor uses his sonic screwdriver to open Sorenson's room and taking the canister as well as finding Sorenson's potion. The potion makes the minerals change. While the Doctor performs these tests on it, Sorenson comes in, his own natural self. The Doctor tells him to keep away -- using the canister.

Salamar takes a neutron accelerator, warns Sarah and Vishinsky off, and threatens them.

The Doctor explains Sorenson is ill: the vaccine cannot keep protecting him against anti quark penetration -- the vaccine set up a cycle of change, even though it protected Sorenson for a short time. His tissues are hybridised and the next change could be the final one. "You and I are scientists, Professor. We buy our privilege to experiment at the cost of total responsibility." He gives Sorenson the canister and stares at the wall. The Doctor sadly says yes to the Professor asking if the hypothesis was false.

Salamar threatens Vishinsky, wanting him to open the hatch. Another man moves to stop him but Salamar shoots the man down. Sarah convinces Vishinsky to let Salamar go. Salamar leaves, mocking Vishinsky as Controller. If Sorenson doesn't get Salamar, the radiation will.

Sorenson goes to Sickbay to eject himself and the canister. He gets into the pallet and puts the canister into the other. As he starts to eject himself, his hand shows immense mutation. His breathing turns ragged. When the Doctor gets there, Sorenson is gone. Vishinsky calls the Doctor, who believes there are two forces aboard. Sorenson left. They explain about Salamar -- he's got to be stopped. 30 minutes to touch down. The Doctor tells them to keep the hatches open and runs out.

Salamar, cracking up, goes to the quarantine room, calling for Sorenson, amid growls. The Doctor yells in the halls -- telling Salamar not to use the accelerator. Sorenson hits Salamar down, coming from near the TARDIS. Salamar is killed by the anti man monster but not before opening the accelerator on it. This makes it mutate further. The Doctor finds Salamar's bony body, dehydrated like the others. Sorenson gone. The Doctor warns the others in the command area: if he hit Sorenson, it could be worse. The Doctor starts up but now he is faced with many anti men -- all semi visible and red glowing like the monster on the planet.

Vishinsky and Sarah worry about the Doctor, who bangs on the door to the control room. They let him in. Vishinsky puts the accelerator back in place and shuts down all the hatchways, "It may hold them." He explains they have multiplied. On the screen Sarah watches the hatchways going down. They are duplicates of Sorenson: pure anti matter--the power boosted and it multiplied. The solarium is attacked and they hear men scream -- seven men in there dead. 16 minutes to impact. The Doctor takes the gun and says, "I'm going out and I may be some time," a Laurence Oates quote. The Doctor moves through the halls to the quarantine room, ridding the air of more anti men monster forms. He finally finds the Sorenson original and drags him into the TARDIS after shooting him with the ray stunner.

The Doctor sets the TARDIS to vanish from the Probe ship. He also locks Sorenson in a metal lock that is attached to his wrists and ankles. Even so, the beast man awakens.

Acceleration of the Probe ship continues to increase. The monsters are all around the control room. With only 6 minutes, Vishinsky needs Sarah's help to get the forcefield equipment to lay a band around the control center to keep the monsters out.

In the TARDIS, Sorenson is bending his metal bonds.

Sarah and Vishinsky race out of the control room, get the equipment and run from more Sorenson monsters, the outlines of the creatures all they can see. The monsters are coming through the doors -- without breaking them. Smoke comes through also.

Sorenson attacks the Doctor with the metal bonds and the TARDIS materializes, the fight continuing outside the TARDIS near the black pit on Zeta Minor. Sorenson falls into the hole and the Doctor tosses the canister in also.

As Sarah and Vishinsky are besieged on the flight deck, the monsters vanish and the ship slows down and stops, still on full power and it moves away from the planet, gaining height. The Doctor has done it. Sarah moans, "Yes but where is he?"