The Cruellest Month by Louise Penny
It's Easter, and on a glorious spring day in peaceful Three Pines, someone waits for night to fall. They plan to raise the dead! When C. I. Gamache of the Surete du Quebec arrives the next morning, he faces an unusual crime scene. A seance in an old, abandoned house has gone horrifically wrong and someone lies frightened to death. For in idyllic Three Pines not all is as it seems. Toxic secrets lie buried, and something terrible has finally clawed its way out. And even Gamache has something to hide. One of his own team is preparing to betray him. But who is it? And how far will they go to ensure Gamache's downfall?