Savigny and Revel investigate the death of Malek Kelkal, a man who has just been released from prison after ten years in detention for robbery. In the victim's pockets, they find two clues: a note that smells of ammonia and a fashion brochure bearing the symbol of a unicorn ...

A band of brigands organizes the robbery of a famous jewelry store on the Place Vendôme. In their wake, they leave the corpses of two teenagers and that of one of their accomplices, Matéo, a computer expert.