Sacked from their jobs as gardeners at a Cambridge college, Wattmore and Griffin are holed up in their isolated cabin in the marshes. Wattmore is a suicidal religious fanatic while Griffin is a more down-to-earth criminal type; bound together by mutual need and exasperation, they behave like an old married couple. To make money, they rent a room to Bolla, a female ex-con. Then it turns out that Wattmore is being blackmailed for a paedophile act, and that he believes Bolla is a witch. Griffin tries to raise money to pay off the blackmail by mugging people in the marshes, while Bolla aims to help her hosts win a poetry competition by kidnapping a Cambridge student.