When police arrest eccentric loner Émile Gassiat for the murder of a wealthy woman in a shabby seaside apartment in Biarritz, Inspector Canonne is certain he has put the killer behind bars.
Now he just needs to prove it.
But he hasn't reckoned with the young man's friends, who bring in lawyer-turned-investigator Larten to head for the desolate out-of-season south-west of France to dig deep into what really happened.
Larten's hunt for the truth takes him back to the bustle of Paris as he seeks to demonstrate that the man in prison is innocent, despite all the evidence – and to uncover the true killer behind a series of bizarre murders.