The film premiered in the United Kingdom in April 2001. Dimension Films, which in October 2001 acquired the rights to distribute the film theatrically in the United States, never did so; it was instead released direct-to-video nearly two years later, by Dimension's then-fellow Disney subsidiary Buena Vista Distribution. The film was shot at Bray Studios and various locations around southern England, including Downside School in Somerset.
The film opens with the appearance of a dishevelled, blood-soaked Liz (Thora Birch), one of four private school pupils, also including Mike (Desmond Harrington), Geoff (Laurence Fox), and Frankie (Keira Knightley), who have been missing for 18 days. Liz is interviewed by a psychiatrist, Dr. Philippa Horwood (Embeth Davidtz), and describes what has happened to the four.
Liz describes how she told Martyn (Daniel Brocklebank) about her unrequited love for Mike; Martyn promised to help, as he and Liz were best friends. Martyn took his four classmates, musician's son Mike, his best friend Geoff, Liz and popular girl Frankie to an abandoned underground nuclear fallout shelter, where they decided to stay in order to avoid a school field trip. The four students climbed into the shelter, Mike reluctantly, and Martyn locked the door shut.
When Martyn was due to release them, the locked-in students belatedly realized they were trapped and began to turn on each other. Then they discovered that Martyn had hidden microphones in the shelter. Voice-acting, Frankie pretended to be sick, while Mike and Liz pretended to hate each other because Liz had said that this was what Martyn wanted – he had been in love with Liz "since we were eleven". The plan apparently worked, as one morning they woke up and the hatch was open. They all climbed out, and Liz described how Mike hugged her, thanking her for saving them.
However, soon after Liz finishes her story, the psychiatrist tells someone on the phone that she does not believe Liz's story, while Liz waves happily to her from the window behind her.
Martyn has been taken into custody for questioning in regards to Liz's story and the psychiatrist brings Liz back to her home. Martyn begins telling the police a completely different story, claiming that Liz and Frankie orchestrated the scheme, to allow Liz to get close to Mike, and Frankie to spend time with Geoff. The police are forced to release Martyn, despite their belief he is guilty, because they can find no evidence. In the meantime, Liz is experiencing flashbacks of the true events in the hole. Martyn comes to see her, angry and distraught that she has framed him. She runs from him through the garden and approaches a weir. Martyn cries, and Liz hysterically says that she knew they would let him go because they could not prove anything. She strokes his neck, but what happens next is not revealed.
At their next meeting, Liz tells the psychiatrist that she cannot remember what happened, however hard she tries. The psychiatrist is persuaded to take Liz back to the hole. Once inside, Liz reveals the truth: Liz had locked herself and her comrades in as a last-minute change to an adolescent plan to win Mike's affection – a spontaneous response to the realization that both Geoff and Mike were attracted to Frankie and had both slept with her. Her obsession with Mike led Liz to believe that, with time, she could win him over, and that locking the door bought her time. Their sojourn in the bunker was initially meant to be a booze and drug party, but when they realized that they could not get out anymore, the mood quickly turned sour. Frankie soon ended up dead from side effects of her bulimia.
The remaining three gradually ran out of food and water. Before Liz can tell Mike that she had the key, Mike discovers that Geoff was hoarding Cola in his bag, and kills him in an uncontrollable outburst of violence by smashing his head against the concrete floor. Reduced to two, Liz suggested a suicide pact, whereupon Mike professed his love for Liz, prompting Liz to climb the ladder towards the shelter's entrance and unlock the door. Perched on a landing high above the shelter's floor, she told Mike she had had the key all along; she had done it all for him. Mike, overwhelmed by the events of the past few days, angrily rushed up the ladder towards her, but the ladder broke and Mike fell to his death, crushed by the broken ladder.
The film then cuts back to Liz and the psychiatrist, Liz concluding that since Mike is dead, he can never leave her. Dr. Horwood asks her to make an official statement which would corroborate Martyn's version of events, although Liz refuses and it is revealed that Liz has murdered Martyn. The police then arrive at the bunker and Liz begins screaming for help as if the doctor was trying to hurt her. The body of Martyn is fished from the river where he had previously chased Liz and the key is found in his pocket, therefore placing guilt on Martyn and the police attribute his death to suicide.
In the end, Liz is allowed to go free. The film ends with her sitting in the back of an ambulance, smiling at the doctor, which turns into a somewhat sinister look.Thora Birch – Elizabeth "Liz" Dunn
Keira Knightley – Frances "Frankie" Almond Smith
Desmond Harrington – Michael "Mike" Steel
Laurence Fox – Geoffrey "Geoff" Bingham
Daniel Brocklebank – Martyn Taylor
Embeth Davidtz – Dr. Philippa Horwood
Steven Waddington – DCS Tom Howard
Kelly Hunter – DI Chapman
Anastasia Hille – Forensic Pathologist Gillian
Nick Hamm began casting actors at the end of 1999. Hamm described newcomer Keira Knightley as a young version of Julie Christie. To prepare for the role, Thora Birch visited an English public school. Principal photography lasted six weeks and took place around London and southern England. Specific locations included Downside Boarding School in Somerset and Bray Studios. The film was shot in Super 35 format.
The film received mixed reviews. On Rotten Tomatoes, the press's critics gave 50% positive reviews. Michael Thomson, in a review for the BBC, said the film was a "dark, grisly adventure" influenced by William Golding's novel Lord of the Flies, with the hole substituting for the island setting. He criticized the camerawork and some of the dialogue, but praised Thora Birch.