Sam Wichner is thirty-one years old. In two days, he is to marry Véra, who works in the same office as he does at the bank. Maryvonne, an employee of Monsieur Teufminn, a diamond merchant, discovers his corpse. He was murdered after having been robbed of a million pounds worth of diamonds. She decides to recruit a detective to find the loot and thus share a hefty insurance payout. She employs Sam Wincher because, five years before starting work at the bank, he was a detective who advertised on books of matches. During his search for the diamonds, Sam encounters Natacha, the defunct diamond merchant's mistress; Ludovic, a pyrotechnician conductor; Johnny, a deaf-mute painter; Madame Teufminn, a blooming widow; Eric, madame's chauffeur and lover... Everyone chases after Sam to make him confess where the diamonds are hidden, even though he has knows as much as anybody - which is to say, nothing at all. He is also unaware that it's Véra who killed Teufminn...