The TARDIS picks up an intergalactic distress call transmitting from 21st-century Earth, and Captain Jack responds to it, thus committing the Doctor to investigate. The signal’s strength increases as they approach; presumably the alien crew have picked up Jack’s response and are warming up the ship for departure. The TARDIS materialises near a stone circle on the Novrosk Peninsula in Siberia, and when the Doctor and his companions emerge, they are confronted by soldiers led by Colonel Oleg Levin; the Russians have detected the energy pulse from the alien signal and have sent Levin to investigate, fearing that there may be a leak in one of the decommissioned nuclear subs at the abandoned naval base. The Doctor uses his psychic paper to convince Levin that he and his friends are here on official business, and Levin explains to the Doctor that he visited the naval base 20 years ago, when it was closed down at the end of the Cold War and the civilians who had helped maintain the base were abandoned to eke out a living in the middle of nowhere. Levin also reveals that the scientists at the base used to conduct research into biological weapons -- which may explain why his men have just found a dead body in the stone circle, a man wasted away to skin and bones.

The village’s police constable, Sofia Barinska, arrives at the stone circle to investigate the death; Levin finds her oddly familiar and concludes that he must have known her mother, as she’s too young for him to have known 20 years ago. Sofia identifies the dead man as Pavel Vahlen, a 19-year-old whose girlfriend, Valeria Mamentova, is also missing. Levin assigns Captain Jack and his second-in-command, Sergeyev, to search the woods for the missing girl. The brash American soon clashes with his dour Russian counterpart, but they work together nonetheless and soon find Valeria, who seems to have aged decades overnight and is in a catatonic stupor. Sergeyev dismisses her as beyond help, but Jack supports her back to the stone circle, where Sofia somewhat embarrassingly suggests that this may be the work of a vourdoulak, a type of Russian vampire.

Levin’s men take Valeria and Pavel’s body to the research base, where they meet the four staff members remaining on a base that once housed 50 scientists: project director Igor Klebanov, students Boris Brodsky and Catherine Kornilova, and administrator Alex Minin. Minin used to be the party political officer, in charge of reporting cases of treason and free thought back to Moscow; nobody likes him much, and for some reason, when they mock him, they make jokes about monkeys. Levin orders Jack and Sergeyev to lead the patrols checking the subs for leakage; before doing so, Jack drops off the catatonic Valeria at her home, and is disturbed by her father’s numb reaction to his daughter’s condition. Sergeyev reluctantly accompanies Jack to the docks, where the soldiers split up to examine the submarines, unaware that a shining blue blob has just oozed its way up out of the sea onto the docks...

Back at the research base, the Doctor determines that something has drained the life force out of Pavel’s body; presumably, the same process began with Valeria but was interrupted. However, the energy spike that the Russians detected was too powerful to have come from the life force of just one body, which implies that there may be others out there. The Doctor tries to analyse a sample from the stone circle, but Klebanov is unco-operative, apparently angered by the interruption to his routine. The Doctor thus visits Minin to ask for supplies, and catches a glimpse of a tattoo on Minin’s arm. Minin admits that he feels guilty about his actions as political officer, and has accepted that the other villagers shun his company. Isolated, he’s made a hobby of researching this area’s history, and he confirms the Doctor’s suspicions that there have been other, similar deaths in the past -- some as recently as two years ago.

At the Doctor’s request, Rose accompanies Sofia back to the village. Sofia reports Pavel’s death to his father, who does not take the news well. Vahlen has already lost one close friend in the past, a man named Chedakin, who shot himself when he was recalled to Moscow -- presumably because Alex Minin had reported him for speaking his mind. After delivering the bad news, Sofia takes Rose to the village’s inn; there, Rose meets Nikolai Stresnev, who maintains the submarines’ diesel generators in order to provide the town with power. Stresnev suggests that Rose visit the blind Giorgi Zinoviev, an old man who claims that he can see into the future. Sofia dismisses Giorgi as a crank, but Rose visits him in any case, and is unnerved when Giorgi identifies her as English and casually claims that he will one day be killed by a man with a bad wolf on his arm. When Rose asks Giorgi what else he can see, he tells her that he can see Stresnev returning to one of the submarines to repair its generator -- and that he can see something crawling up out of the sea and draining the life out of Stresnev’s body. Even as he speaks, the generator dies and the lights in the village go out.

The Doctor visits Catherine’s laboratory to analyse the sample from the stone circle, and must circle around the entire base to get there, as there doesn’t seem to be a direct route through the centre of the building. He also asks Catherine why Minin is teased about monkeys, and she explains that he once kicked up a fuss about a bureaucratic error that suggested the institute had paid for live specimens that never arrived. This happened at around the same time that Chedakin died, and as the villagers were particularly angry with Minin at the time they seized on this incident to mock him. The Doctor studies the stone sample and finds that the lines of quartz inside are strangely regular, almost like a printed circuit -- and when Catherine picks up the sample, her hand shows signs of aging. The Doctor’s hand also ages when he touches the sample, but unlike Catherine’s, it returns to normal within minutes. Apparently the stone is keyed to draw the life force out of humans only -- but if the stones need to draw energy, why not take it from every possible source? As the Doctor muses, Klebanov passes through the laboratory, and after resting his hands near the stone sample he briefly speaks with the same slang as the Doctor, almost as if he’s picked up the tendency from him.

Rose returns to the inn and tells Sofia of Giorgi’s prediction. The policewoman reluctantly agrees to investigate, and when they reach the docks, they find Stresnev’s body, drained of life just like Pavel’s. Rose cries out in surprise, attracting the attention of Jack, Sergeyev, and a soldier named Razul -- and when Sergeyev tries to contact the other soldiers, he finds that communications are somehow being jammed. Razul agrees to fix the submarine’s generator and restore power to the village, while Sofia and Rose return to the inn to warn the others of the danger. However, as they approach the inn, Rose notices Sofia scratching her ear, a nervous tic that Stresnev had earlier displayed. She and Sofia then hear a strange scraping sound and spot a weird, pulsing blue light in the distance; Sofia heads off to investigate, but it’s Rose who finds the withered body of one of Levin’s soldiers. She is nearly attacked by a gelatinous blue blob, but escapes and informs Sofia. Unnerved by these weird events, Sofia tells Rose that she wants to check out the stone circle again.

Back at the base, the Doctor tells Minin that he needs to exhume one of the previous victims. Only Fedor Vahlen has access to the equipment that will dig through the frozen ground, but he won’t help Minin, whom he blames for Chedakin’s death. However, the Doctor convinces Vahlen that more people will die like his son unless he helps to find out what’s happening. Vahlen thus digs up one of the graves, and the Doctor opens up the coffin to find that the body has been reduced to a small pile of goo. Vahlen then asks permission to see his son, and the sympathetic Minin leaves him alone in his office while preparing the body -- but when he returns, he finds that Vahlen has gone through his files and learned the truth about Chedakin’s death. Although the official verdict was suicide, Chedakin was shot in the back of the head. As the furious Vahlen departs, the Doctor checks the base’s logs and discovers that the deaths have coincided with periods of radio interference. Klebanov refuses to co-operate with the Doctor’s investigation, but Minin tells the Doctor that Klebanov has always been irritable; he was at the base long before Minin arrived, and he’s the one who started mocking Minin for inquiring about the monkeys, even though Minin had clear paperwork evidence that the live specimens had been paid for and supposedly delivered.

Razul repairs the village’s diesel generator, but then he, Jack and Sergeyev hear something slither across the sub’s hull, and return to the hatch to find it coated with goo. A blue blob oozes down into the sub, lashing its tentacles out at them, and they retreat, only to realise that the goo on the ladder means that a second blob has already entered the submarine. Trapped between the two blobs, they try to hide beneath the hull plates, but Razul panics, giving away his position. As the blobs pry up the plates and suck the life force out of Razul’s body, Jack and Sergeyev try to retreat, but can only flee deeper into the submarine. Jack thus orders Sergeyev to hide in a cabin, wait for Jack to draw off the blobs and return to warn the others; Sergeyev agrees to do so, now regarding Jack with more respect. Jack lures the blobs to the torpedo room at the end of the submarine and locks himself in -- but he can find no other way out, and is trapped inside as the blobs begin to batter down the door.

Rose and Sofia return to the stone circle, where Sofia reveals that she knows the stones normally draw the life out of their victims when activated -- and if they are acting of their own accord, something has gone wrong. Sofia tries to test her theory by forcing Rose towards one of the stones, but Rose overbalances, causing Sofia to topple into one of the stones herself and age decades in a matter of seconds. Rose flees, but catches a glimpse of the now elderly Sofia apparently heading towards the Institute. Unwilling to return to the docks and face the weird blue blobs, Rose instead goes to Sofia’s house to investigate further.

Inside Sofia’s home, Rose finds a strange device built into a chair and connected to pipes leading beneath the house. Sofia then returns home, but Rose hides from her, and sees Sofia checking a secret panel in the floor. Unable to last much longer, Sofia staggers to the electric chair, and as Rose had suspected, the power that floods through the chair when switched on restores her to youth. While Sofia is occupied, Rose flees through the secret panel, which leads through an underground tunnel to a spacecraft buried in a sea cavern. Jack surfaces from the water, explaining that he opened the submarine’s torpedo tubes, flooded the chamber and swam out. He and Rose study the spaceship, and find a mummified alien body and a room full of bodies like human-ape hybrids. Sofia then arrives and tries to kill them, but Jack shoots her in the chest; however, this only slows her down. He and Rose retreat into the cave and shut the ship’s door; they are thus cut off from the tunnel back to Sofia’s house, but they find another set of stairs that lead up to a locked supply cupboard in the research base.

The Doctor hears Rose and Jack trying to get out, and opens the door for them. When they tell him their story, he sends the incredulous Minin to fetch Levin and accompanies his companions down to the spaceship, which he identifies as a craft from the Arcane Collegiate. Presumably, the pilot was killed in the crash, and over the centuries, as the earth shifted, the ship ended up underground. The ship repaired itself, but since its pilot was dead, it assumed that it was missing a necessary component and was still in need of repair; thus, it transmitted an automatic distress signal and raised its antennae, the stone circle, to collect energy for its power banks while it waited. Presumably it was built with a failsafe that prevents it from draining the life out of intelligent beings, but it appears that Sofia -- and others -- have tampered with the ship, circumventing the failsafe and forcing the ship to draw the life out of other human beings and feed it back into Sofia and her cohorts so they can remain young. However, things are now out of Sofia’s control, because when Jack responded to the ship’s distress call, it began to prepare for departure -- and since the antenna wasn’t providing it with enough energy, it created blobs from the same material as the stone circle and sent them out to collect as much energy as it needed to launch. However, because the ship has been tampered with, it is no longer capable of flight -- and it will simply continue to send out its remote drones until it has destroyed the human race.

Sofia then emerges from hiding and attacks the Doctor and his friends, but they overpower her, and the Doctor reveals that Sofia is already over a century old. When she found the ship, it fed information into her mind so that she could repair it, and taught her how to drain life from others so that she’d live long enough to complete her work; however, she abused the knowledge in order to extend her life, and has crippled the ship beyond repair in the process. Levin and his men arrive just as Sofia overpowers the Doctor, but their bullets have little effect on her, as she’s brimming with stolen life force. She kills one of the soldiers, takes his gun and chases the Doctor out of the ship, back to her house and down to the docks -- where he is attacked by more of the ship’s remotes. However, his life force isn’t human enough for them, and they turn aside and attack Sofia instead, draining the life out of her body and feeding it back into the ship.

The Doctor takes Levin and his men to the inn to explain the situation to the villagers. Giorgi arrives, claiming that he can see the blobs coming for them, and the Doctor realises that Giorgi is attuned to the psychic wavelength that the ship uses to communicate with the remotes. If Giorgi can send information as well as receive it, he can lure the remotes into a trap. The blobs attack the inn, but Rose helps Levin to get the villagers to safety while the Doctor and Jack hold off the blobs. The villagers retreat to the research base, where they block the road with a gigantic bonfire, building it with the excavator that Vahlen uses to dig up the graves. Meanwhile, the Doctor takes Giorgi to the base’s clean room, an isolated quarantine chamber, where he places Giorgi in a trance so he can focus on leading the blobs into the villagers’ trap. Minin offers to keep an eye on Giorgi, but Klebanov, realising that Minin is under some strain, takes over while Minin fetches himself a coffee. The Doctor returns to the bonfire, where he explains to Rose that the remotes transmit energy directly to the ship without converting it to heat; thus, a sudden temperature change should be enough to kill them. However, Rose is more concerned with Giorgi’s prediction, which he has repeated, that he will be killed by a man with a bad wolf on his arm.

Jack sees Valeria’s father evacuating to the research base without her, and realises that the weary old man, sickened by what has happened to his daughter, has left her behind. Furious, Jack rushes back to the village to save Valeria himself. On the way back, he is reunited with Sergeyev, who is impressed by Jack’s bravery and agrees to help. Sergeyev stands guard outside the Mamentov house while Jack enters, but the blobs descend upon Sergeyev and drain him. Jack manages to get Valeria to safety, but the now-elderly girl is walking too slowly -- and just as they get within sight of the pyre, the villagers set it aflame, trapping Jack and Valeria between the burning pyre and the approaching blobs.

On the other side of the pyre, the Doctor and Rose see that some of the blobs have circled around the pyre and are closing in on the research base. Someone has gotten to the hypnotised Giorgi and given him false instructions. The Doctor calls Minin, who tries to get into the Clean Room to wake Giorgi -- and ends up trapped in the airlock, as the pass code has been changed. The Doctor returns to help Minin while Rose tracks down Vahlen, the only man with the tools to get through the airlock. As Vahlen returns to the base, Rose sees Jack and Valeria on the other side of the flames, and realises that the blobs are closing in on them; she thus drives Vahlen’s digger through the pyre, scoops up Jack and Valeria and drives them back to safety with seconds to spare.

The Doctor tries to free Minin from the airlock with his sonic screwdriver, but only succeeds in fusing the controls. The inner door jams halfway open, and Minin has little choice but to draw his gun and start shooting, hoping that the noise will wake Giorgi from his trance. As he does so, the Doctor notices that Minin has a tattoo of a wolf on his arm -- and when Giorgi fails to stir, Minin has little choice but to shoot and kill him in order to prevent him from drawing the blobs to the research base. A stray bullet punctures one of the canisters in the clean room, releasing toxic gas -- but when Vahlen arrives, he refuses to rescue Minin. Furious, the Doctor reveals the real meaning of the memos that Vahlen skimmed over earlier; it wasn’t Minin who was spying for the party, it was Chedakin, whose friendly persona was a front to trick the other villagers into dropping their guard around him. Minin found out the truth and killed Chedakin before he could betray his “friends,” but allowed the others to believe that he was the party official rather than reveal that their friend had been playing them for fools. Shaken, Vahlen helps the Doctor to open the airlock and pull Minin to safety before the toxic gas reaches him.

Levin’s men retreat to the base with the villagers as the blobs close in, and the Doctor finds more blobs blocking the stairs, preventing him from reaching the ship to shut it down. The villagers need a place to defend, and the Doctor notes that the centre of the institute doesn’t appear on any of the plans. Klebanov claims that part of the base was sealed off after a bio-contaminant leak in the 1950s; nevertheless, they have nowhere else to go, and the Doctor thus orders the troops to dynamite their way into the sealed-off section. The blobs break into the base before the soldiers are ready, however, killing Brodsky and closing in on the other villagers. In order to buy the soldiers time, Minin douses himself with vodka, sets himself aflame with his cigarette lighter and runs towards the blobs, sacrificing himself to drive them back.

The soldiers break through the wall to reveal a laboratory containing the mummified bodies of scientists -- who are still alive. Klebanov reveals that Sofia showed the ship to them back when this base was first constructed, and like her, the ship planted knowledge in their heads so they could help repair it. However, the ship only had enough energy to keep Klebanov and Sofia young, and the scientists couldn’t afford to sacrifice too many people to the stones, for fear of drawing attention; thus, most of the scientists sealed themselves up in the base and waited for Klebanov to find some way to restore them all to youth. The monkeys that caused Minin such trouble were used in illicit experiments, but the scientists who fed on the monkeys’ life force became the grotesque hybrids whose bodies were hidden in the ship. However, the scientists have found a way to transmit energy directly from the ship into their bodies, with no need for a direct wired connection -- and now that the ship is fully active again, thanks to Jack, the scientists can put in motion a plan to feed it enough energy to ensure their immortality.

While Klebanov crows over his triumph, Jack and Lt Krylek plant more bombs and blow open an exit from the sealed-off laboratory. Levin and his men escort the villagers out to safety, shooting at the scientists to cover their escape; Klebanov is grievously injured but survives despite the damage to his body. In the confusion, the catatonic Valeria is left behind, and Klebanov decides to keep her as a hostage, since Jack has shown concern for her safety. Rose sees this, however, and follows them out of the laboratory at a distance. Meanwhile, the Doctor leads the survivors to the docks, having worked out that the scientists intend to launch one of the “decommissioned” missiles from the submarines. Levin and his men cover the ice with fuel and set fire to it, holding off the blobs while the Doctor swims to the underwater cave and conducts some sabotage in the spaceship. In the confusion, Jack and Catherine see Klebanov and his men boarding the St Petersburg; Klebanov was in charge of decommissioning that particular sub’s missiles, and presumably he deliberately neglected to do so. When the Doctor returns, he sets off to confront Klebanov, and orders Jack to lure the blobs back to the laboratory, using himself as bait.

Rose follows the zombie scientists onto the St Petersburg, and tries to rescue Valeria while they are preparing for launch; however, the catatonic Valeria stumbles into the door on her way out, drawing the scientists’ attention. Rose flees to the missile bay, where she is confronted by three undead scientists -- and is rescued by the Doctor, who slipped on board through the secondary hatch. When Klebanov and his fellow scientists catch up, the Doctor makes one last appeal to their humanity; their plan to grant themselves immortality will work, but as a side-effect, the fallout from the nuclear blast will sweep across the steppes and kill millions in the nearest inhabited cities. Nevertheless, Klebanov refuses to halt the countdown -- but when it reaches zero, nothing happens. Before confronting the scientists, the Doctor sabotaged the fuel hoses, and although the readouts indicated that the missiles were being refuelled, they were actually being filled with seawater.

Jack bursts in and knocks the gun out of Klebanov’s hands before he can shoot the Doctor. The scientists’ bodies then begin to waste away to dust, as Jack has done his job and lured the blobs to the laboratory -- and the wireless transmitter that the scientists were using to draw life force from the ship’s power banks. The blobs, programmed to seek out the strongest sources of energy, were drawn towards the transmitter -- and by trying to feed from it, they’ve created a feedback loop, and are sending the ship energy that the ship itself is transmitting. With each cycle, a little more energy is lost, until the scientists and blobs crumble to dust and the ship dies, powerless.