At the local park Sarah, Maria, Luke and Maria’s father Alan watch Clyde rolling about on his skateboard. As the group recall the first time they met, Clyde falls from his board and Alan takes the opportunity to show off his own skills with a skateboard, a leisure pursuit he abandoned when he got married. Maria seizes the opportunity to take some photographs of her friends, but when she tries to take one of Sarah he friend feels some sort of disturbance:

“Somebody just walked over my grave”

Returning to Bannerman Road Maria, Luke and Sarah go to the attic. Sarah asks Mr Smith the Computer to track the progress of meteorite K67, which he claims is on collision course with Earth. Maria is shocked but the others remain calm. Luke explains that the meteor is approaching through a blind spot in the radar of major authorities, and only they can stop it. Sarah reassures her worried friend that Mr Smith will be able to avert catastrophe by creating a magnetic pulse, thus bouncing the projectile back into space. Collision will take place the following afternoon.

Despite being somewhat confused that Sarah would save the world and not expect thanks for it, Maria seeks comfort in the fact they will be safe. Sarah asks Luke to leave and make some tea whilst she and Maria talk. She presents her young friend with a gift, a metallic box given to her by a Verren Soothsayer they helped get home a few days previously; he told her to give it to the person she trusted the most

Mr Smith has already examined the object and claimed it is nothing more than a puzzle box, but nonetheless Maria spends that night in her bedroom trying to get inside. After much effort she manages to make progress; twisting a corner of the cube so it sits at an angle before sliding one half of the box slightly out of place. She retires to bed; still holding the puzzle whilst outside the hooded figure from the park arrives. It raises a ghostly hand and points at Sarah Jane’s car, causing it to disappear.

In her bedroom Maria clings to the box whilst the figure, a hideous-looking monster with no eyes and a mouth of pointy teeth, its hand again. This time it points at Sarah’s house, causing all of the lights inside to go out. The creature disappears and across the road Maria awakens with a fright, dropping the box.

The next morning Maria arrives downstairs to find that her father has retrieved his old skateboard from the attic. He hands his daughter a birthday card for her to sign, addressed to a woman named Andrea. Maria appears to have no idea who this might be, but signs it nevertheless and then goes across the road to meet Luke. When she knocks on the door it is answered by a blonde woman with a faint cockney accent. Maria asks where Sarah Jane and Luke are but she doesn’t understand whom she is talking about, yet recognises Maria perfectly.

Maria leaves her and returns home. She asks her dad what has happened to Sarah Jane but he doesn’t recognise the name either, claiming that the blonde woman, Andrea, has always lived in the house across the road. To try and prove her father wrong she shows her the photos she took in the park yesterday, but when she views them she finds none of them contain Sarah or Luke, just Clyde, her father, Andrea and herself.

Maria then checks the address book on her mobile phone, but finds that both Sarah Jane and Luke’s names have gone. She phones Clyde but he appears to have little recognition of her, only that she is a girl from his school and they met once at the park the previous day. Like Maria’s father he has no idea who Sarah or Luke are, and believes Maria to be mad when she warns him of an approaching meteorite.

Maria returns to the house across the road and after being welcomed by Andrea she runs inside, finding the décor of different rooms has changed. Alan arrives and he and Andrea follow Maria upstairs to the attic, which is now empty, all of Sarah’s possessions have gone and Mr Smith has been replaced by a large mirror hanging on a wall. Alan apologises to Andrea for the intrusion and takes his daughter home; unaware that once they have gone Andrea appears to recall the name Sarah Jane Smith.

Back at their home Maria and her father look over the previous days photos again, before Alan attempts to assure Maria that Andrea has always lived in Bannerman Road by showing her photos of their neighbour helping them to unpack the day they moved in. Maria struggles to understand what is going on, and takes offence when her dad tells her to forget Sarah Jane and the meteor, which he believes to be inventions of her mind.

Maria tells him that somehow Sarah Jane has vanished and everyone has forgotten her, but somehow she has been protected. She searches for Sarah’s name on the Internet and finds a poem written about a girl of the same name, claiming that she died on 13th July 1964.

The pair then goes to the Library to follow up their research and find an article claiming the girl died after falling from a pier, and was accompanied at the time by another girl named Andrea Yates. Alan thinks that Maria is simply pretending to know Sarah Jane, presumably having heard the story before from Andrea. Maria is upset by her father’s scepticism but is then shocked when she sees the names of Sarah and Andrea switching places in the article before her. Moments later she hears Sarah Jane calling to her for help, but it appears the noise is only apparent to her.

She and Alan leave the library and to stop her father from worrying about her Maria pretends that her stories about Sarah and Luke are, as he believes, fiction. She returns to Andreas house to apologise but takes the opportunity to question her about the accident in 1964. She claims that Sarah Jane was never meant to die, and that it was at that point that the world was somehow changed. Andrea orders her to leave but before she goes Maria swears that she will find some way of making sure history takes the right course.

Visibly shaken, Andrea runs up to the attic. She searches in an old storage box and pulls out a metal cube identical to the one Maria was given by Sarah before she disappears. A disembodied voice calls out to her, telling her to “Remember”. She looks around, stepping before the mirror hanging upon one of the walls. The hooded creature that stalked Bannerman Road the previous night appears as an image in the mirror, standing behind her. It tells her again to remember and sure enough Andrea proclaims that she remembers what she did the day Sarah died, the day the creature gave her the box. It asks why she calls upon him now and Andrea explains that Maria Jackson knows what has happened, she is aware that history has changed.

She breaks down in tears, again recalling the agreement she and the creature made back in 1964. She asks him to make Maria forget Sarah Jane again but he tells her he is unable to, somehow she is protected. He explains that he is unable to kill her either but she can be removed, as Sarah Jane was. He tells her that he requires her agreement to take action and she grants it, and once this is done he tells her that she must help him by separating the girl from her father.

Maria sits in her bedroom alone, when Sarah calls out to her again. She wanders over to a mirror and finds her lost friend concealed within. She asks how she can help stop the meteor but Sarah cannot tell her anything, continuing to call out for help.

Andrea lures Alan away from his house by asking him to help hang a banner for her birthday party later that day. Maria meanwhile recovers the metal box, which has fallen under her bed and realises it is that that has protected her. She runs downstairs to find a small snarling alien creature waiting for her. She flees from the house, dropping the box en route. The creature chases her, and they eventually end up under a nearby railway bridge.

Alan returns home to find the box Maria dropped. He picks it up at the precise moment the creature under the bridge opens fire on Maria, shooting two small electrodes onto her jacket, causing her to disappear. A blue light engulfs him and he flinches it pain, but soon the ordeal is over. He looks around, wondering what is going on. Soon his ex-wife Chrissie arrives telling him they must hurry to Andrea’s party. Alan worries what might have happened to Maria, but Chrissie doesn’t understand what he is talking about. Alan bluntly explains their daughter has gone missing but Chrissie laughs, they never had a child.

Maria reappears on a stone walkway suspended amongst the clouds. The creature that captured her leads her along the myriad of paths, but she manages to disconnect the electrodes it shot at her and she disappears from view again. She returns to Earth but not where she left, this time she is by the seaside. She looks around in disbelief before approaching two schoolgirls for help. She introduces herself as Maria Jackson, and one of the girls shakes her by the hand. “

Maria assumes that the girl standing next to Sarah is Andrea, and when she grabs a nearby newspaper she discovers it is 13th July 1964, the day of the accident. She tries to warn the to girls not to venture onto the closed pier, knowing that the blank-faced creature must be about to arrive (recognising the reason she appeared in 1964 is because the creature must have visit there as well to switch the two girls at the moment of the accident).

Andrea, assuming Maria to be mad, drags Sarah away and when their backs are turned the small creature that captured Maria arrives. It shoots the two metallic electrodes from its gun at her and once again she is taken away. Meanwhile, Sarah and Andrea have been trying to get past the locked gates of the pier. Eventually they succeed but not before Sarah notices the sudden disappearance of their brief acquaintance.

Maria reappears in a white void. Her captor releases the two electrodes from her lapel and then leaves. Looking around anxiously, Maria is jubilant when she finds Sarah Jane, who has been deposited in the void as well. The two embrace and Sarah explains that they are in limbo, an empty space.

Back on Earth Alan and Chrissie continue to argue. Alan tries to convince his estranged wife that they once had a daughter but she denies it, claiming that if they had they might never have split up. Alan then realises that the metal box he found must have protected him, just as it had done for Maria. Now knowing that Maria was telling the truth and that Sarah Jane must indeed exist, he leaves the house, despite Chrissie showing him pictures of the day he moved home, depicting himself, Andrea, but no Maria.

In the void Sarah recalls the day Andrea died when she fell from the pier, revealing she had always pondered that it could have been her that fell, and now the timeline has changed her thoughts have become reality. Maria interjects and claims that if Sarah ceases to exist on Earth then the meteor must still be on the way, and no one can stop it but her.

Sarah asks how Maria still knew of Sarah when the rest of the world had forgotten. She explains about the box and Sarah realises the Soothsayer who gave it to her must have known what was due to happen, and thus gave it to her to give her some chance of being saved.

Maria confesses she dropped the device back on Earth then inquires about the creature that captured her. Sarah explains that it is a Graske but theorises that what has happened is too powerful for such a creature to manufacture, it must be a slave for something else. Suddenly a ghostly voice rings out, calling her name. She warns Maria to stay where she is, then walks off to find the source of her summons, disappearing into the fog.

In Bannerman road Andrea welcomes the guests at her birthday party, whilst in the void Sarah confronts the hooded creature that changed the timelines. It lifts its hood to reveal its blank face, punctuated only by a fanged mouth. She asks its name but it claims it has none, it is “nothing”. Explaining that it feeds off of chaos in order to survive, the creature tells Sarah that she is the key to the food it needs. Without her in existence the meteor will collide with Earth and then the creature can draw energy from the resulting disarray.

It waited for just the right moment to snuff out her life, and to ensure the course of history was not changed until it deemed fit to interfere, he turned away the creatures Sarah has fought on her own on Earth; the Slitheen, the Gorgons, even the Bane. It tells her that since the Bane never came to Earth her son Luke was never born and therefore he now exists in ‘The Forgotten Places’, even further out into the void than Sarah and Maria.

Sarah asks why the other creatures were expelled from Earth and it explains that the results of their plans do not result in chaos; they are the fruits of revenge or the lust for power. The meteor represents none of those things, it happens by chance, and thus brings true pandemonium. Sarah is hurt by the fact the creature doesn’t care about the billions of people and animals that walk the Earth, but it insists it cares about her, for her life was so important to its plans. It explains that on 13th July, the day of the accident, he saved Andrea’s life by switching her and Sarah so that it was her who fell from the pier. However he could only do so once Andrea had agreed to let Sarah Jane die in her place.

Sarah seems hurt and protests when the creature turns to leave. It plans to return when the Earth has been destroyed and claims that she will still be of use to him, with her memories he can locate the Doctor and delete him from history, the amount of chaos such a deed would bring would create massive supplies of energy for him. He fades away as Sarah screams out in protest against his plans concerning her old friend, but her cries are unheard.

At Andrea’s house Clyde arrives, shortly followed by Alan and Chrissie. Meanwhile, Sarah returns to Maria and comforts her, claiming there is nothing and no one who can help them, they’ve been forgotten. On Earth Clyde turns on Andrea’s television to view a news report, which claims a meteor is about to collide with Earth. Alan recalls what Maria said to him about such a happening and begins to worry, but Clyde claims the projectile will miss the Earth.

Andrea, calmed by Clyde’s declaration, goes to the kitchen to fetch more glasses. Alan follows her and confronts her about Maria and Sarah, but she claims not to know of them. She changes her tune when he shows her the metal box that protected him, and warns him that they cannot be saved. He demands to know hat has happened to them and she takes him up to the attic, where she explains what happened the day of the accident.

She and Sarah ran onto the pier, and when she leaned on the barrier to look out at the sea it gave way, causing her to fall. She grabbed onto a ledge hovering over the rough waters below, yet despite Sarah’s efforts to help her back onto the pier she couldn’t hold on any longer. It was then the hooded creature intervened, calling to her and telling her that it could save her life if she gave her permission for Sarah to die instead of her.

She agrees to the proposition and in a flash the scene had changed, now with Sarah dangling over the sea whilst she stood safely on the pier. She watched as her friend dropped from the ledge to her death, and was then confronted by the creature and its Graske slave. The creature presented her with a metal box identical to the one Alan now possesses, and told her that she would forget what had happened so that she could live a full life.

For over forty years she had forgotten about the transaction, but Maria’s visit made her remember again and for that she had to be sent away as well. Andrea begins to break down in tears and she confronts the mirror hanging on the attic wall. The hooded creature appears within it and tells her that with her agreement Alan can be removed as well. Distraught, she gives her permission and grabs the metal box from Alan’s hand. Suddenly the Graske arrives and chases Alan from the house.

In the living room Chrissie, Clyde and the other guests continue to watch the new report, which claims that the RAF will destroy the meteor before it reaches Earth. Chrissie turns to see he ex-husband being chased by the alien creature but assumes it is merely a man in a suit. She returns to the living room where the news reported explains that the missile strike intended to destroy the meteor has failed.

Alan manages to evade the Graske and capture it, tying it up in his own home with the curtain cord, demanding to know where his daughter has been taken. Meanwhile, the guests from the party rush outside to watch the meteor approach. Andrea realises what Maria said to her that morning, that Sarah Jane was the only one who could avert disaster.

The Graske shows Alan how to retrieve Maria using its gun, and sure enough seconds later his daughter is back beside him. Outside Chrissie suddenly remembers her daughter and runs off to find her. Inside the house Maria tells her father that they must save Sarah in order to save the Earth. He repeats the action with the gun that retrieved his daughter but Sarah doesn’t appear. Maria theorises that is she herself was returned to her home, where she belongs, Sarah will be returned to where she belongs; her attic.

They hurry outside unaware that the Graske has freed itself, teleporting away. Up in the attic Andrea tries to seek solace in her metal box but is distracted when another apparition appears in the mirror; Sarah Jane. They welcome each other before Maria and Alan arrive. Sarah explains she cannot return whilst Andrea lives, and explains that only her childhood friend can bring her back, by retracting her previous agreement and dying instead of Sarah back in 1964.

Andrea protests after Maria claims she was meant to die, claiming that she has lived her life to the full and made the most of existence. Sarah cuts in and claims she had done the same before she was betrayed, and tearfully begs Andrea to change the timelines back and save her son. However, her friend fears being wiped from existence only left forgotten and refuses. Sarah protests that Andrea was never forgotten, it as her accident that showed her how precious life was, and as a result she fought to defend it ever since.

Andrea’s eyes begin to fill with tears as the hooded creature arrives. She confronts it and orders it to retract their agreement. It tempts her, claiming she will die as a result but she retorts that she has been dead for forty years. She turns to Sarah Jane in the mirror and bid her farewell, before shattering the mirror with the metal box given to her by the creature.

Suddenly the timelines are restored. Back in 1964 Andrea resumes her position dangling from the end of the pier, saying goodbye to her friend once more with the words “Remember me”. She falls and in the present day Sarah and Luke are returned to Earth, finding themselves in the reformed attic with Sarah and Alan. Outside the meteor roars ever closer and Sarah calls upon Mr Smith to help. He activates the magnetic field and the meteor is deflected back into the skies, the Earth is saved.