Laurène shortens medical leave to investigate a murder. In a flashback to 57 BC, Roman soldiers suffer a mysterious attack.

While Nounours analyzes the images of the victims, Laurène returns to the library to search about ancient Celtic rituals.

In the lake, a bees attack leads to a sinister discovery. Laurène holds Jonas to find out what he knows about the figure in the forest.

The full moon leaves the city bustling. Hermann struggles with ghosts from the past, and Siriani does not miss out on the opportunity to inspect the quarry.

Laurène finds a surreal crime scene, entitled to a piano in the middle of the forest. Cora tries to figure out what the end of Roman was. Garnier investigates Siriani's past.

Laurène remembers details of her kidnapping while trying to get help for Nounours. Siriani makes a disturbing discovery.

With the team embezzled and the day of the dead ever closer. Laurène begs for reinforcements. Strangely agitated dogs lead her to a new corpse.