In their fourth outing, Tess Gerritsen's heroine duo, Dr. Maura Isles and Det. Jane Rizzoli, investigate the gruesome slaying of Lori-Ann Tucker, discovered with her head and left hand chopped off. Crucial to the case, though, are the satanic symbols and the word peccavi (which means ''I have sinned'' in Latin) scrawled all over the blood-drenched scene. A related homicide leads them to the Mephisto Foundation, a secret organization obsessed with tracking down evil. Loaded with outlandish murder details and a tenuous good-versus-evil plot, The Mephisto Club is a quick read that feels real enough to be worthy of a nightmare or two.