The Mephisto Club is the 6th of Tess Gerritsen’s Rizzoli/Isles series. On Christmas Eve, Rizzoli and Isles are called to a horrific murder scene where the female victim has been decapitated and dismembered. During the autopsy, however, they realise there must be more than one victim as the left hand does not match the arm. And a call has been made from the victim’s phone to Dr Joyce O’Donnell, the neuropsychiatrist who has made a career of defending serial killers. Before they can discover to whom the hand belongs, one of their own, a female police detective, is murdered in the backyard of a house where Joyce O’Donnell is dining. Symbols and words at both crime scenes, made with an unusual ochre clay, point to a Satanic element; or do they? When events in Isles’ personal life coincide with the same symbols on her own front door, the action really starts to heat up. And Rizzoli has problems of her own with the way her parents are behaving. Gerritsen gives us two back stories which will have the reader convinced they know who the culprit is, although everyone but Rizzoli starts to wonder if their perp is, in fact, human. Gerristen touches on celibacy in the Church, secret societies, Satanic possession, mid-life crisis, and whether evil can have a physical form. Once again, Rizzoli provides some humour; the story is full of suspense and has plenty of twists and turns to keep the reader engrossed. Another Gerritsen winner.