Sherlock Coco, famous detective, tries to thwart the machiavellian plans of the trio of shock. Croquignol, Ribouldingue and Filochard must be extra vigilant, but the profit motive is too strong. As a corollary, the famous pink diamond is also of interest to their legendary enemy, Jo Papillon. But always inventive, they will work out multiple scams and tricks to reach their goals.

Although suspected and hunted down by policeman Sherlock Coco and inspector Hector, the Pieds Nickelés (Croquignol, Filochard and Ribouldingue) manage to save the legacy of Monsieur Miradoux, who will be very grateful to them.