Clerk Freddie Clegg (Terence Stamp), an avid butterfly collector, wins a football pool and buys a country house with a large basement. He then kidnaps art student Miranda Grey (Samantha Eggar), a longtime crush of his, after trailing her in a van. Freddie locks Miranda in the basement, and buys her clothes and books, so that she can get to know him. They initially agree that she will stay at the house for a month, but Miranda fears what will happen when the time comes for her to leave.