The elderly Rani listens as the boy, Adam, explains that he lives across the road and after having heard the stories about her at school, could not resist the urge to investigate. He watches as she takes a box from the windowsill and sorts through its contents - photographs of the people she used to know and love - her parents, Sarah Jane Smith, Luke, and Clyde - now all gone.
She remembers Sarah and how she changed her life, something she never thanked her for because she never thought that one day the adventures all four of them shared together might end. She recalls the monsters she witnessed back before aliens were commonplace visitors to Earth - when not everybody knew everything.
Adams asks how she came to be alone in the attic and she claims it was simply because of a single mistake she made when she was a teenager.
Back in 2009 the teenage Rani, having found a report of strange lights in the sky on the Internet, hurries over the road to see Sarah, Luke and Clyde and tell them about her discovery. Unfortunately, they have already uncovered this and managed to confirm with Mr. Smith the computer that it was simply a bolt of lightening. Rani then listens as her three friends recount the latest adventures of their old companion Maria, who is now living in America and assisting the government with alien cover-ups.
Feeling dejected Rani returns home where she finds an e-mail on her computer from an old friend of her own - Sam Lloyd, whom she lived near before moving to London but lost contact with when he stopped returning her calls. Now having found something he would like her to investigate, he has broken his silence.
She returns to her old hometown to find Sam - more irritable than she remembers - who takes her to the now-abandoned amusement park. He claims that recently, four people have disappeared after entering the grounds, all homeless and therefore passed over by the police. Soon after a young boy went snooping around one of the old rides and claims to have seen a demon haunting the attraction. Having heard from Rani that she now spends her life hunting aliens, Sam asks her to investigate.
Rani is keen on the idea but finds herself going on alone - despite wanting someone to solve the problem, Sam has no interest in doing so himself. He wanders off as Rani makes her way inside the park, making a log of her findings on a voice recorder. Soon she is discovered by the park's caretaker, Harry Sowersby, who tells her to leave.
She bluffs her way into his office by claiming to have twisted her ankle, and once they are inside she begins to question him about there being someone or something living in the park. He rebuts the idea but when a ghostly voice is heard announcing "playtime is beginning", Rani's suspicions are confirmed and she leaves to find the source of the noise. Left alone, Harry turns to his wash basing mirror, where a haunting red face appears and recites the incantation once again.
Rani ventures outside and sees four people - human but with red eyes - marching across the park and onto various rides. The attractions begin working again and the possessed punters dutifully enjoy their outing.
Back on Bannerman Road, Sarah realises that Rani has gone missing and is worried she may be responsible after dismissing her friend's story earlier that day. Realising they need to find her, Clyde prepares to search Rani's house, under the pretence of having left a book there.
At the amusement park, Rani refuses to answer calls from her friends whilst the spectacle continues. The demon's voice announces that "playtime is over" and the attractions all come to a halt.
Having searches Rani's room, Clyde returns to the attic and shows Sarah and Luke the e-mail Rani received from Sam. Sarah is hurt that Rani has revealed all of their secrets to the boy and calls on Mr. Smith to investigate Sam Lloyd, whom they discover is actually living in a care home after his parents died in a car crash.
Meanwhile, Rani records her findings just as Harry arrives, telling her again that she should leave. Refusing, Rani heads towards the ride the four abductees came from before mounting the rides. She heads inside with Harry following close behind, just as playtime begins again.
Elsewhere, Sarah, Luke and Clyde arrive at Sam's care home - and he seems to have been expecting them. Shrugging off their pleasantries he tells them he will reveal Rani's whereabouts:
"She's with her."
Rani eventually finds her way to a hidden room at the heart of the abandoned ride, there she finds a girl standing with her back to her. This, Harry claims, is his own little girl, Eve, and she needs somebody to play with. He swiftly locks the door leaving Rani and Eve together. Rani panics but then turns to face her new companion - the red-skinned demon.
Having learned little from Sam other than the mystery of the amusement park, Luke elects to stay behind and talk to him whilst Sarah and Clyde go in search of Rani. Sam watches them go.
Rani tries to speak with Eve, who communicates telepathically. Reading the young human's mind, Eve reassures Rani that she need not worry so much about proving herself to her parents and her friends - she knows they love her, and that they are proud of her. Rani is astonished.
On their way to the park, Sarah and Clyde bicker about their friendship and who discovered who - Sarah insists she chose her allies but Clyde claims she had no choice. He teases that her memory may be failing with age, and runs ahead leaving Sarah to smile.
Rani asks Eve about her own childhood and reluctantly she reveals that she is an orphan. Many years ago a war between two alien races, neither of them her own, raged across time and space, and due to her people being able to read time lines, they came under attack and were exterminated. Her parents managed to save her by placing her in a ship and sending her off into space. It is so long ago now, that she can no longer recall her own mother's face.
As Sarah and Clyde arrive outside, Rani watches the homeless people forced to play on the rides. She asks why they do so and Eve claims that she makes them - she saw that they were sad and alone and so made them be happy again.
Outside Clyde tries to talk with one of the players, but he receives no reply. Soon Harry arrives.
Back at the care home Luke talks to Sam about losing the people they love. Sam claims that Luke is lucky to still have a mother, despite losing Maria; he has no other friends or any family to care for him. However, as he turns to his mirror he insists that he is not alone; and immediately the red face that spoke to Harry appears before him in the reflection.
Whilst Sarah and Clyde try to find out from Harry where their friend is gone - the old man insisting she is still safe - Rani urges Eve to let her human playthings go. Eve ignores this and instead returns to reading Rani's mind, seeing the events of the morning in the attic and telling her that despite how she felt, she needs Sarah, Luke and Clyde. Reacting badly to the intrusion, and once again rejecting a mobile call from her friends, she offhandedly claims:
"I wish they'd just leave me alone"
In the office Harry leads Sarah to his mirror, seemingly at the command of the face in the reflection. Likewise, Sam grabs Luke and presents him to his own mirror; the face inside wants to know more abut the extraordinary mother and son.
At the abandoned ride Eve presents Rani to yet another looking glass, and offers t show her the future. Rani protests, claiming it is wrong to know. Eve goads her, claiming that is a doctrine imposed by Sarah Jane. Convinced, Rani agrees to look into the glass, but when she does the future she sees is not a happy one.
"Oh god, make it stop. Please, no, I can't become that. I'm so lost, so alone. The mad old woman of Bannerman Road."