A young Argentine mathematician comes to Oxford for an internship, where fate brings him together with the famous scientist Arthur Seldom. Together they are trying to solve a series of crimes that are somehow mysteriously connected with the teachings of Pythagoras and his followers. The mysterious killer seems to challenge Seldom to an intellectual duel, demanding to prove in practice the correctness of his theories. In search of clues, the heroes turn to the history of forensics and magic, to the achievements of traditional psychology and to the practices of ancient sects.