Congo Requiem - Jean-Christophe Grangé - book

You don't choose your family, but the devil chose his clan.
 
While Grégoire and Erwan track down the truth to Lontano, in the heart of African darkness, Loïc and Gaëlle confront a new killer in Florence and Paris.
 
Unbeknownst to them, they all have a meeting with the same enemy: The Nail Man.
 
Among the Morvans, all roads lead to hell.