Below Suspicion — John Dickson Carr

The Death Worshippers
They all were so very different. The rich old woman with her collection of weird books. The handsome man with his mysterious powers. The beautiful blonde with her come-hither look, and the sweet young thing with something wild about her. Yet as were involved in the hideous happenings spawned by a strange and terrible cult. And Dr. Gideon Fell knew that the fiendish slayings would go on and on -- unless he discovered the creature, master of lechery and murder, who led the unholy group in its delirium of hate