Colombian Luccio and his girlfriend Angie move into a respectable part of Berkshire, learning that Ron and Helen, the previous owners of their house, died mysteriously. Angie discovers that their neighbours, estate agent Roy and his wife Jane, high court judge Charles and his bickering wife Carol and Bilbo, a conceptual artist and his partner were all members of a wife-swapping circle who usually met at Ron and Helen's house. Luccio reveals himself to be a policeman and is curious as to how Ron and Helen died, lining up all the suspects.

A sequel to 1974's Challenge, in which the title character is assigned to gather incriminating evidence against his rival in the state senate, but his assignment gets complicated when the rival hires a group of killers to rub him out.