Infuriated by receiving the wrong piece of film, statistician James Richards arranges for the errant researcher, Sharon Newton, to be sacked. Realising that he is responsible, Sharon contacts James and demands his help. She has obtained a mysterious piece of monochrome film which, while superficially a collection of street scenes, seems to show the abduction of a woman. The film abruptly cuts off, instructing the viewer to see 'The Hedgerows of England'. As this film has been registered 'classified' by the Ministry of Defence, Sharon, obsessed by the identity of the woman, needs James, with his official credentials, to obtain it for her.

James, both infuriated and fascinated by Sharon, tracks down the film, but a visit to an old tram depot and an archive beneath Oxford Street proves frustrating, as the film has now been moved. He and Sharon chase it to a landfill site, where they notice a police presence, and then to the incinerator at Edmonton, where they manage to rescue it before it is burned. But upon viewing the film, they find that it is very poor quality, revealing only a dark image of a woman in front of some kind of tribunal. A card at the end tells them that the next film to look for is called 'Hop-Picking in Kent'. James, despite yearning for the attentions of his ex-wife, is not entirely unhappy to find his comfortable life disrupted by the search for the film, and he wakes up, after a drunken evening spent at a video duplication service, at Sharon's house, where he discovers that she has a young daughter. Needing to go out to work, she leaves her daughter with James.

Taking the baby out to meet his ex-wife, James is cornered by two officials, who beat him up and demand to know the whereabouts of something he has found. Shaken, he goes to see his city friend Anthony, who advises him to go home and forget about it. But Anthony also drops a hint that he too has been questioned, and James realises that he is in serious danger. Returning to his house, he finds it has been searched and realises that the officials want some medical records which he idly picked up from the landfill site. After an unexpected encounter with them, James manages to escape and is reunited with a distressed Sharon, who has been worried about her daughter. She explains that her obsession with the film lies in her limited education and a related desire to teach herself as an adult.

Meanwhile, a friend of Sharon's does some illicit searching for her in the archives and discovers the film 'Hop-Picking In Kent'. Within the bland information film is a full version of the mysterious film, featuring a different woman along with a man. Some kind of emergency has occurred and left the participants dead. Moving forward in time, the film documents the birth of an abruptly aborted government project named Magnificat. The women from the original film then reappears, sitting in a location which James recognises: an official building which has re-opened as a café. The film ends with the woman reunited with a horribly scarred man and confronting the cameraman, asking why he is filming. James suggests that this was the result of an accident with nuclear power which has been hushed up and that the café was once a secure convalescent unit. He also wonders why the film was made in the first place. James and Sharon decide to keep the film secret and he throws the offending medical records into a bin. Meanwhile, somewhere in London, a cleaner has her break in an isolated room where the remnants of Project Magnificat are still stored.