When a university librarian is mugged and robbed of his winnings outside a casino, DS Alistair MacRae assumes that it was an opportunistic crime, But when other incidents involving him occur, MacRae wonders whether there are other reasons for the crime When the man is murdered, MacRae is sure he knows who is responsible. But DCI Ian Forsyth has a better solution arrived at by the use of logical deduction. When the fingerprints from the front man in a financial scam are found at the scene of a murder, it is assumed that the victim was his immediate superior in the scam. When two further people with shady financial backgrounds are also killed, MacRae believes that a man who lost heavily in the scam is responsible. But Forsyth arrives at a different conclusion, is able to interpret a clue left by the last victim and thus comes up with the proof that will convince a jury that his solution is the correct one.