A man calls and asks for Maigret, from a café and says he's being followed by someone trying to kill him. He says that Maigret knows his wife, Nine. Before he can finish he hangs up, calls back from another. He tries again from various cafés, till finally the calls stop. That night, his body is found in the Place de la Concorde, his face badly beaten, stabbed to death. Someone had seen it pushed out of a car. Although his picture is published, there is no clue to who the man is until a woman who'd seen a yellow Citröen comes forward, and the man's own café, Au Petit Albert is discovered, as well as his name, Albert Rochain.
With the absence of clues, Maigret decides to reopen Albert's café, using an inspector, Émile Chevrier and his wife. The ruse works, and a suspicious man is spotted and followed, but before he can lead them to his lair, he is shot down, apparently by one of his own. He is identified as a Czech laborer, Victor Poliensky. A raid is planned and executed in the Rue du Roi-de-Sicile district, and at the Hôtel du Lion d'Or, a Czech woman, Maria, is found in labor. From the testimony of the proprieter, it becomes clear that she is one of the band of Czechs who had brutally committed murder and robbery on farms in the north, the Picardy killers.
Colombani of the Sûreté Nationale joins the hunt, as the two cases are combined. A stakeout of the hospital where Maria is kept results in two more gang members, one shot by another, and own captured, leaving only one, plus the unknown leader. Investigation at the race track at Vincennes leads to the identification of a young actress, Francine Latour, frequently seen with a heavy-betting Czech, Jean Bronsky. Latour is a dancer at the Folies-Bergère, and a capture is finally made in front of her apartment. Maigret goes to visit Nine Rochain, hiding out in Corbeil, and while there the last member of the gang, Serge Madok, is arrested.
The review of this Book prepared by Dana Samson