In her room, looking out at the starry sky above, Maria tries to explain to her father Alan the lure of life with Sarah Jane. She recalls the adventures they shared together; battling the Slitheen (some of whom she noted escaped before their defeat) and then the Gorgon, who turned her dad to stone.

In her attic, Sarah adjusts a telescope so that she and Luke can view a formation of lights in the sky unseen for four thousand years. Maria enters and tells her about her father’s intentions to move home. Sarah comforts her, reasoning that he cannot be blamed for wanting to keep her safe. Soon Alan joins them and tries to convince his daughter they must go, but she manages to change his mind, and he finally accepts he must adjust to the revelations put before him. Soon the light shw begins and Sarah looks out in awe

“The universe is smiling on us Alan”

“Let’s hope it always does”

The next day Luke sits in his living room reading a book with the television playing in the background. On the screen is a news report showing two parents pleading for information concerning their lost son Ashley, whom they believe has been abducted. After a while Sarah enters the room and watches the report, whilst over the road Maria and her father do the same.

A picture of Ashley is shown and much to everyone’s shock, he is revealed to be the spitting image of Luke. Sarah rushes to the attic and calls Mr Smith, who has been monitoring the news. He claims that to determine whether or not Luke really is Ashley he must scan him, but Luke protests that he created by the Bane, he has no memory of life before he awoke in the Bubble Shock factory.

Sarah insists Mr Smith examine him and the result of the test confirms that Luke is indeed the missing boy. Sarah claims it must be a mistake, saying he cannot be human, as he has no navel. Mr Smith tells her it may have been removed by the Bane when they captured him because to them it served no purpose. As Luke embraces his mother, Sarah asks her computer if there is any chance the scan may be wrong, but he insists the likelihood of failure is around four billion-to-one.

Some time later Alan and Maria sit around their dining room table. Chrissie enters boasting the fact she always had suspicions that Sarah Jane was not all she seemed, and tells them that she has called the police. Maria is distraught and runs outside, where she is joined by Clyde, who has heard the news as well. The Police soon arrive and Sarah calmly opens the door, asking them to wait for her to say goodbye to Luke. She returns inside and tries to calm the young boy, who is frustrated he has no memories of his would-be parents.

She tells him he must go, to be with the people he belongs with. She leads him outside where Ashley’s parents arrive and embrace their lost boy, who still has no recollection of them. Sarah tries to explain she had no idea of the child’s past life and is taken away in a police car. Luke and his parents leave soon after.

At the police station Sarah is informed by the Chief Inspector that UNIT have managed to secure her freedom and she is permitted to leave, whilst elsewhere in the city Luke arrives at his old home. He is bemused by the revelations his parents present him with concerning his life before he knew Sarah, finding his hobbies and tastes have since changed dramatically. He retires to his room but the door is locked behind him, leaving him trapped. Downstairs his parents sit watching the television. They switch over the channel and are bathed in a green light. They lean toward the screen and laugh:

“Xyloc are you there? We’ve got the boy”

Back on Bannerman Road Maria arrives at Sarah’s home. She approaches her friend, who stands in the living room and they embrace, but after a second Sarah pushes her away. She explains that Mr Smith has confirmed Luke is indeed the child of the two parents from the news report and then claims that it is not the only mistake she has made; children must play no more part in her life. She reminds Maria that her life is dangerous and for her own safety she must forget her, as should Alan and Clyde.

She shows Maria to the door and the young girl leaves. Sarah then returns to the attic, somewhat crushed by the ordeal of loosing both a son and a close friend in the same day. She reclines on a chair but is interrupted by Mr Smith, who emerges from his hiding place in the chimney without summons. He tells her that she, like all things in the universe needs a purpose, and explains to her that he has discovered the Pharos Institution, a research facility, have discovered a way of manipulating kinetic energy using alien technology. Sarah decides she should investigate the company, now without any children to look after, and prepares to leave.

Back in his room, Luke is unnerved when his father arrives. He asks why he was locked in his bedroom and he claims it was to stop him running away again. He then tells his son that he will not be allowed to go to school, even to see his friend Maria and Clyde. Luke asks how he knew their names despite him never having mentioned them, but his father simply leaves and locks the door, claiming he will never see them again.

Clyde and Maria meanwhile return to their lives at school, upset by recent events but understanding Sarah’s pain at loosing a son. Clyde decides that they should visit Luke and opts to skip school in order to see him, and his friend follows. They make their way to the courtyard before Maria is caught and sent back to lessons, but Clyde succeeds in jumping the fence and running off.

Sarah arrives at the Pharos Institution, a grand building inhabited by a group of scientists. She is shown around by Professor XXX, who encourages the publicity Sarah can give the organisation and thus guides her around some of their laboratories. In one they witness an experiment involving a headset that takes the latent psychic abilities of all human beings and utilises it so as to move objects, in this case a basketball.

After witnessing the ball burst the Professor explains they are having trouble with MITRE, the name for their energy focus stabilisation. She then takes them to see Nathan Goss, a child genius who has been working on MITRE. Sarah finds the young boy remarkably rude to his adult company, and before she leaves she turns on him

“I used to know someone your age who could wipe the floor with your intelligence Nathan, and wipe the floor with you to.”

She turns and leaves with the Professor, but Nathan has the last word

“We’ll see about that”

Clyde eventually arrives at Luke’s new home, but is turned away by his mother. She dismisses his claims that Luke is not theirs and presents him with a photograph taken at Ashley’s birthday party. Unsatisfied but defeated Clyde leaves, unaware that upstairs Luke is pounding on the window of his bedroom trying to get his attention. Failing to do this he begins rummaging around his bedroom, looking for a ruler.

Clyde reaches the local park and calls Maria, explaining to her his disbelief at the situation concerning Luke. He claims the photo given to him may be faked, and decides to take it to Sarah Jane.

Luke uses the ruler to break the lock on his door and sneaks downstairs. In the living room his parents sit giggling, when suddenly Nathan Goss enters:

“We’ve got a problem”

Sarah returns to her attic where Mr Smith explains the profile of Nathan Goss, who has been called the “Young Einstein” by some critics. She fobs the boy off as an “obnoxious brat”, and claims there is something about him that made her blood run cold. The computer goes on to explain that MITRE is beyond even Nathan’s intelligence and that the Pharos headsets could, in the wrong hands, destroy planets. He tells her that to find out more about the technology he will need one of the headsets, and Sarah agrees to go and steal one.

Nathan explains to the two adults before him that Sarah Jane has seen the Telekinetic Energiser, and fears she may know too much. They protest at his bluntness but he insists the mission they are working toward is his, and Sarah must not be allowed to interfere. Luke’s mother claims an entity known as the Xyloc told them Sarah might interfere and not to worry, but Nathan is dismissive of the Xyloc’s trustworthiness. Suddenly they hear Luke coming down the stairs and chase him outside, managing to drag him back into the house before he can escape.

They escort him back to the living room where his would-be parents disclose their true identities. Reaching up to their foreheads they unzip their skin to reveal they are in fact Slitheen, now housed in slim-line skin-suits. Luke then turns to Nathan, who eventually reveals he too is one of the creatures, the same infant he encountered when they tried to destroy the Earth only to be stopped by Luke, Sarah, Maria and Clyde.

Clyde arrives on Bannerman road only to find Sarah departing in her car. He finds the spare key to her door and ascends to the attic, where he manages to summon Mr Smith. He shows the computer the photograph of Luke and it confirms it is not real.

“It is fake. I faked it”

Clyde seems stunned by this revelation, and Mr Smith tells him:

“I am a Xyloc. I have a purpose. And you Clyde, are a part of it”

Alone in the darkness Sarah Jane returns to the Pharos Institute. She approaches the building and makes her way inside, where she manages to find one of the headsets. After narrowly avoiding the security guards she takes the device and returns outside, only to find the security alarms have been set off. Disarming them with her Sonic Lipstick she runs off, followed into the woods by a guard on a motorbike. She once again uses the Lipstick in order to dismount him then carries on her way.

Back in Bannerman Road Maria tries to contact Clyde using her mobile phone and is annoyed to find he doesn’t answer; unaware Mr Smith has abducted him. Clyde finds himself in a dark space surrounded by floating numbers; pondering where he has been taken.

Maria confides in her father that she fears Clyde may be missing, explaining to him that he skipped school to try and find Luke. She decides she must try and find her friends, and her dad agrees to help. They arrive at the house belonging to Luke’s false parents and manage to get inside via an open window. They look for clues that might explain who the abductors really are, but Maria’s questions are soon answered when they find a skin suit hanging on a nearby door…Luke has been taken by the Slitheen.

Clyde begins to believe he may not be able to return home. He calls out to Mr Smith, who fobs off his questions and tells him that he, and the rest of the human race, will soon die. Suddenly Sarah’s voice rings out and Clyde realises he is in fact inside Mr Smith, and can only watch in vain as Sarah hands over the headset she has stolen, unaware of Mr Smith’s true identity.

Maria and her father return home to find Chrissie waiting for them. Alan gives his daughter an excuse to leave whilst he and his ex-wife go inside the house. Maria goes across the road to see Sarah, and tells her about the Slitheen.

Meanwhile, the Slitheen (in human form) take Luke to the Pharos Institution, knocking out the guard who greets them at the gate.

Chrissie leaves Alan to examine his malfunctioning computer, which he soon discovers is being accessed by Clyde from within Mr Smith. He sends a message warning that Mr Smith is evil and Sarah Jane must be warned. Alan runs across the road and warns his neighbour, who is up in her attic with Maria. They escape just in time to avoid being shot by the rogue computer and return to Maria’s home.

Mr Smith manages to stop Clyde from contacting the others but compliments the young man on his ingenuity. He toys with his prisoner then knocks him out.

Alan tries to make contact again but fails. Instead he asks Sarah Jane here Mr Smith came from and she explains that he began life as a crystal discovered at the site of Krakatoa. After examining the object she discovered it was in fact a memory cell from a crashed space ship, and by communicating with he laptop it revealed it could help her track alien life on Earth, and so designed and built Mr Smith.

Sarah tells her friends that they must find Luke, and deduces that the Slitheen are behind the telekinesis experiments at Pharos, planning to use the headsets to tap into the superhuman levels of telekinetic ability hidden within Luke and sell it to galaxies where such science is highly prized. However, if they manage to drain the abilities from Luke’s mind it will kill him. She hurries outside, Alan and Maria following quickly behind.

At the Institute Luke is strapped into a chair and a headset is placed on his head. The device is energised and the boy begins to shake. However, soon the computer begins to overload and Luke manages to use the energy to escape, closely followed by Nathan. A chase ensures but eventually Luke manages to escape.

Sarah, Alan and Maria stop at a chip shop and arm themselves with vinegar with which the fight the Slitheen. They arrive moments later at the Institute and confront the Slitheen, who explain that Luke has gone. Nathan forces them to put down their weapons after threatening to kill Maria, then joins his family as they try to contact the Xyloc, alias Mr Smith.

The creatures then explain that Mr Smith contacted them some time ago after observing what had happened to Nathan’s father the last time the family encountered Sarah and Maria. Wanting to help them take revenge Mr Smith helped them to develop the headsets in order to regain their fortunes and get back at Sarah by killing Luke.

However, after Sarah explains that Mr Smith asked her to steal a headset, it becomes apparent he has double-crossed his partners in crime. He used the Slitheen to build the telekinetic energiser, and Sarah to steal it for him. Now, as Sarah realises, he will use Luke, whom he knew would escape and return to Sarah’s home in the hope he would be safe there. Sure enough Luke arrives in the attic, where Mr Smith is waiting for him.

Nathan moves to attack Sarah but his parents stop him, believing Sarah could help save their lives. She explains that Mr Smith once told her that the headsets could be used to move planets, and theorises that the Xyloc’s plan could be devastating to the planet Earth.

Mr Smith locks the door of the attic and forces Luke to put on the headset. When he does the computer begins using his latent abilities to move the moon, aiming to force it to collide with Earth and wipe out mankind.

Back at the Institute Sarah manages to persuade the Slitheen to help her save the planet (and indeed themselves) by destroying Mr Smith. Alan, a computer expert, begins trying to find a solution but is interrupted by a call from his ex-wife, who is stuck outside as storms erupt across the world. She shouts above the howling wind, claiming she needs to be with him and her daughter. The line goes dead whilst all over the world fires and floods sweep the continents as a result of the gravitational disturbance.

Alan resumes his work and reveals he has access to a computer virus that could wipe out the entire banking network of the world, explaining to Sarah that she is not the only one with unorthodox contacts he downloads the virus onto a disk, and gives it to her.

The Slitheen help Sarah return to her attic by giving her their teleport system, and she arrives to find Luke still under mental attack. Mr Smith tells her that by instigating the oncoming collision he will be able to release the rest of the Xyloc from their prison below the planet’s surface. He may have been separated from the rest of his race (who crashed to Earth millions of years ago as a meteorite) but he is still in contact with them. Ever since Sarah built him he has been planning to destroy the Earth, and she has helped him. As an act of mercy he returns Clyde, but then aims a gun at her.

“I told you Sarah Jane we all have a purpose. Yours is to die so that the Xyloc will live. After all what life do you have, alone in your attic?” As he speaks Sarah backs against a safe on the other side of the room and begins entering the combination.

“Alone? You think I’m alone? You think I’m defenceless? Well meet my dog. K9, protect me!”

She flings open the door and K9 rolls into the attic, opening fire upon the Xyloc computer. Amongst the gunfire that ensues Sarah manages to initiate the computer virus, and Mr Smith’s memory begins to erode. Sarah tells him without memories he has no purpose, and without a purpose he cannot destroy the planet. She orders him to release Luke and then gives him a new purpose, to save the Earth. He agrees and sends the Moon back into orbit.

K9 returns to the safe, a portal into space wherein lies a black hole he has been stabilising. Sarah embraces Luke, and soon she stands with him in the garden alongside Clyde, Maria, Alan and Chrissie, all of them looking up at the stars. She explains that Mr Smith will soon reboot with a new purpose, to protect the Earth.