Ruth, a young journalist, is asked by her boss to investigate the Chesterton clinic. There, they run a weight loss program called "Think Thin", presided over by a man called Willis.
At the meeting Ruth witnesses the methods employed by the "Think Thin" program. Willis stands each person up in front of the whole group and shouts abuse at them. He degrades them, making derogatory statements about the state of their bodies, hoping to shame them into dieting.
That night Ruth has dinner with one of the members of "Think Thin", Ben Faraday. Ben explains how he has been put on a special protein and citrus fruit diet for two weeks and that Willis ordered him to take in some extra fat for the citrus fruit to work on. He also discloses to Ruth that he has been given some special pills to speed up his metabolism.
Ben says goodbye to Ruth, and Ruth gives him her phone number by writing it onto his hand. He drives off. While driving he starts to have hallucinations. This affects his driving, and he swerves all over the road, eventually crashing into a tree. A mysterious man dressed as an undertaker is on the scene in seconds to look at the dead body.
Ruth is one of the first people to be notified of his tragic death because of the telephone number written on his hand. At Ben Faraday's funeral, a young man notices the press sticker on her car and asks to speak with her.
The young man, Andrew, who works at a funeral parlour, tells her that he believes there are some strange things going on at Chesterton clinic. He believes that Ben Faraday wasn't inside the coffin that was buried. Andrew asks her if she would like to investigate.
Ruth agrees, and they both break into the church crypt that night. After gaining entry to the crypt, they open the coffin and are shocked to discover, not a body, but a wire frame in the shape of a body.
They then pay a visit to the funeral parlour to see if the body is there. They find a decapitated body, and when Andrew lifts up the right hand, they see Ruth's phone number!
Ruth investigates further and waits outside the funeral parlour to see where they take the hearse. They take it straight to the Chesterton clinic. Mr Rothwell, the owner of the clinic, watches from the window and spots Ruth snooping around. What is going on at the clinic and did Ben Faraday meet with an accident or was he the victim of foul play?..
After discussions with her editor, Ruth gets herself admitted to the clinic and has a consultation with Rothwell in order for her to investigate further.
That night, Ruth sneaks outside to see Rothwell dressed up in a dinner jacket taking a body bag from the clinic and placing it in his car. He is followed to a large mansion where a party is taking place. Ruth enters to find a large dining table laid out for dinner. She is discovered by Sir Humphrey Chesterton, who invites her to dinner. Ruth is introduced to the other guests and is left talking to an old lady who explains how they all met. They were the only survivors of a plane crash and they all meet up once a month. Ruth realises why they all meet up for a reunion and runs screaming from the house.
Ruth goes back to the funeral parlour to find Andrew's dead body on the slab. Willis is there waiting in the shadows and brings a cleaver down on Ruth.