Following the arrest of Delteil's killer, Maigret and his team close in on Olga Borysenko's murderer. However, the investigation lands Maigret in more danger than anticipated, making a powerful enemy who has already outmaneuvered him once before.
On Skeleton Island, Jim leads the search for the treasure as tension and paranoia rise when the island's dark history emerges; jockeying for control they finally reach the fortune - but an unexpected force intervenes before anyone can claim it.