Paris, 1832. A terrible cholera epidemic is hitting Paris, hitting the poor first and spreading panic. The city is gripped by rumors and fear, and the people are murmuring against the measures imposed by the government. While the authorities and doctors are trying to curb cholera, a new disaster is hitting the capital — corpses with stab wounds are beginning to be found in the Saint-Merri quarter. The investigation of mysterious murders is entrusted to the Bureau of Dark Affairs under the supervision of Inspector Valentin Verne. He is assisted by the faithful Aglaya, and two newcomers: A Deceiver, a repentant conman and a master of trickery, as well as Tafik, a former Mamluk of Napoleon's army, a real giant. However, events soon spiral out of control: false leads multiply, scientists are abducted, and Vidocq, who has once again become the head of the Surtay police, finds a way to uncover the Vicar's true identity and answer the question that torments the inspector at night: who did this criminal serve?