Sarah Jane hears a commotion outside her house at 5:00 am, and investigates to find a stunned milkman staring at a Victorian villa that has replaced the ordinary family home at 39 Bannerman Rd. The milkman manages to convince himself that it's a trick set up by a television show, but Sarah can see a shimmering in the air above the walkway, and she catches sight of a flat-screen TV through the villa's windows before lace curtains and drapes suddenly materialise and block her view. She returns home to consult Mr Smith, who determines that the villa is the house that stood on the same site between 1865 and 1969; somehow, it has been displaced in Time, from the year 1884. Mr Smith also confirms that the temporal fluctuations haven't stopped and could spread even further.
According to Luke, the normal house's owners, the O'Briens, are an ordinary family who recently left for a three-week holiday to Australia. While Sarah Jane continues to consult Mr Smith, Luke wakes Clyde and Rani, who help him to seal off the house from curious onlookers using spare police tape and the Vorgat defence emitter. Rani decides to risk peering through the house's windows, and sees that the house's interior still looks like the O'Brien's modern sitting room -- but Victorian-era furniture has begun to appear inside. Rani then suddenly finds herself standing on Bannerman Road in the year 1884, in front of a modern house transplanted into a row of villas. A few seconds later, she is snapped back to the 21st century, and she tells Clyde and Luke that while she felt nothing going back, the return journey made her feel ill.
Mr Smith scans the world media for reports of similar incidents but comes up blank, apart from a report of an extra-terrestrial prisoner who recently escaped from a phase-shift prison in Russia. Rani and the boys then return and tell their story to Sarah, and Mr Smith confirms that he detected a spike of zygma energy at the moment that Rani returned to the present day. This implies that she was deliberately sent back by someone in 1884 who doesn't want to be disturbed at what they're doing. Worse, Mr Smith warns that zygma energy is inherently unstable, and that the growing temporal fracture could cause an explosion that will shatter Time between 1884 and the present day, destroying life on Earth.
Sarah Jane and her friends return to the villa to investigate further, and Sarah Jane spots movement through the window. Luke insists upon accompanying her inside, and they unlock the villa's front door with Sarah Jane's sonic lipstick and step inside. For a moment, they catch sight of a small figure in the O'Brien's hallway, but then find themselves in the interior of the Victorian villa back in 1884. Modern furnishings are scattered about the old house, and upstairs, they can hear a man named Charles and his wife Beatrice searching desperately for their missing daughter May and berating the hapless maid Clara for playing foolish jokes by replacing their furnishings with garish paintings. Luke and Sarah Jane are then snapped back to the present day, where they discover that the small figure they saw earlier was May. Sarah Jane assures the terrified little girl that they'll help her return home, and takes her out of the house to meet the others. She and Luke were able to spend more time back in 1884 than Rani, and Luke theorises that it takes more energy to send two people forward in Time than it does one; if this is the case, perhaps they'll be able to spend even more time there if they use the Vorgat force shield to protect them. May then speaks up, claiming to have seen a bad man in "the spidery place," but she's too frightened to elaborate.
Sarah Jane returns home to consult Mr Smith, warning the others not to enter the house; however, Clyde convinces Luke to go back inside, using the force shield as he'd suggested earlier. Clyde also reveals that he had Mr Smith research the villa's history; in 1884, it's occupied by architect Charles Burden, Beatrice, and May, and their maid Clara, who will put up with her employers' abuse until 1893. When Clyde and Luke step into the house, they are transported back to 1884 and begin searching for the "spidery place". Instead, they encounter Charles Burden, and because the Vorgat shield makes their bodies appear to glow, the terrified architect concludes that these boys are the demons who have taken his daughter. Clara then screams out loud from upstairs, and Clyde and Luke rush up to find that she's just seen her mistress vanish into thin air before her eyes. Charles attacks the boys with a fireplace poker, and when it bounces harmlessly off the force shield, he and Clara flee from the house to fetch help. The boys take the opportunity to search the attic, but this is where Clara lives, and it's free of dust and cobwebs. However, the shadow of a thin spindly creature seems to be sitting on Clara's bed, laughing at them. The force shield then runs out of power, and the shadow swoops forward to engulf them.
Rani and May hear a woman cry out from inside the house, and Rani risks entering to investigate; since May has been swapped forward by the temporal fluctuations, her presence keeps Rani stable in the present day as well. May's mother has appeared inside the house's modern-day bathroom, but the terrified woman can't accept what's happening to her and refuses to answer Rani's questions, insisting that this is all a terrible dream. However, when Beatrice lashes out at the filthy heathens who would put a water closet in the indoor bathroom, Rani realises that the "spidery place" that May referred to was an outdoor toilet.
Meanwhile, Sarah Jane has found an intruder in her attic: a muscular, red-skinned humanoid with three eyes, who reveals that he's been tapping into Mr Smith's power supply for the past ten days. Due to the computer virus that recently compromised Mr Smith's defences, Mr Smith never even noticed that he was powering a time bubble at the O'Briens'. The alien admits that it is the creature who escaped from the phase-shift prison in Russia, but claims that its arrest was a mistake exacerbated by the fact that its name roughly translates into Russian as "Death Kill Massacre." In fact, he's a bounty hunter searching for two genocidal alien war criminals named Efnol and Skak; he managed to catch Efnol first, and since the O'Briens had gone on vacation and their house was located very close to an advanced computer in the form of Mr Smith, he left his prisoner trapped in a stasis bubble in their attic while he went hunting for Skak. However, Skak sent an anonymous tip to the Russian authorities, and while Deathy was dealing with them, Skak travelled back to 1884 and began stretching the bubble back to its breaking point using zygma energy and time pumps. The houses on either side of the stretching point are switching places as a side effect, and when the bubble shatters, Efnol and Skak will ride the temporal feedback to safety while the Earth is destroyed behind them.
Sarah Jane takes Deathy back to the O'Briens', where Rani tells them what she's learned. Skak has kicked Sarah Jane and her friends out of 1884 before they could find him and interfere with his work, but Deathy is equipped with shielding that will protect him. Before he can approach the house, however, the police arrive to investigate the neighbours' reports of youths loitering around a mysterious mansion, and a policeman confronts Deathy, believing that he's a troublemaker in fancy dress. The impatient Deathy teleports the policeman out of his path, but fails to notice that he arrived with a partner, who panics and calls in backup. Deathy is forced to flee from the police, who don't listen when Sarah tries to warn him that they're chasing away the only person who can save the world.
Clyde and Luke then materialise in the front yard, and when they tell Sarah Jane what they've seen, she realises that Efnol is about to break through in 1884. She activates the Vorgat shield's emergency reserve power with her sonic lipstick, and she and her friends enter the house together, reasoning that it will be too difficult for Skak to send all four of them through time at once. Back in 1884, they head straight for the outside loo, where the spindly, stone-like Skak is operating his time manipulator. While Luke and Clyde fight Skak, Sarah Jane and Rani cause the force shield to contract around Skak's time manipulator, crushing it. There is a momentary time distortion as they do so, however, and Efnol then leaps down into the yard from the attic. Sarah Jane realises that she sealed up the machine at the very moment that the time bubble shattered; once the force shield runs out of power, the temporal energy will be released, and the world will end.
Efnol and Skak turn their backs on the helpless Sarah Jane and her friends, but are caught off guard when Charles Burden bursts into the yard with a mob of his friends and neighbours. Upon seeing the aliens, he concludes that the two boys he saw earlier have shed their human guises to reveal their true demonic forms, and before Efnol and Skak can react, the mob descends upon them and begins beating them to death. However, the angry mob then freezes in Time, and Deathy emerges from the outhouse, revealing that Sarah Jane's interference bought him enough time to shake off his pursuit and come back to set things right. Using his own more advanced equipment and the power he tapped from Mr Smith, Deathy has repaired the shatterpoint, and he now pulls Efnol and Skak out of the mob, promising that he will deliver them to the proper authorities for a fair trial. Sarah Jane and her friends linger just long enough to see Beatrice and May emerge from the house to be reunited with the overjoyed Charles, and Deathy then sends them back to the present day. Satisfied, they return to their homes, leaving the police and other bystanders staring in astonishment at the O'Briens' house, which has returned to normal.