On the banks of the Ardèche, near Vallon-Pont-d'Arc, kayakers find the body of the museum president of a recently discovered Paleolithic cave. A 40,000-year-old carved stone was embedded in his neck. To investigate, Captain Manon Ferret-Duval of the research section teams up with her counterpart Riad Lekcir. They must overcome a shared past: she is convinced that her partner's older brother is responsible for the murder of her parents in 1994. Riad has no doubt that Kamel, now deceased, is innocent.

Bill Baker, an American oil-rig roughneck from Oklahoma, travels to Marseille to visit his estranged daughter, Allison, who is in prison for a murder she claims she did not commit. Confronted with language barriers, cultural differences, and a complicated legal system, Bill builds a new life for himself in France as he makes it his personal mission to exonerate his daughter.