A woman is murdered in Oxford. Her body is discovered by two men, Arthur Seldom (John Hurt), a prestigious professor of logic, and Martin (Elijah Wood), a young graduate student who has just arrived at the university hoping to study with Seldom. It quickly becomes clear that this is the first in a series of murders, all of which are announced by the murderer with strange mathematical symbols. Professor and student join forces to try and crack the code, and thus begins an elaborate puzzle, in which nothing is as it seems, and the truth is elusive.