GARFIELD REEVES-STEVENS has a habit of blending genres and in his latest work, Dark Matter (Doubleday, 375 pages, $24-95 cloth), he successfully mixes the thriller and science fiction, with the emphasis on science. When a series of grisly murders occurs, the modus operandi of which is craniotomy, a smart but emotionally vulnerable Black female Los Angeles detective gets involved in the investigation. The murderer, and were told pretty early on who it is, is a sociopathic Nobel Prize-winning physicist who gains inspiration for his top-secret experiments by massaging the brains of his victims. He also spends a lot of time despising the inferior physicists he`s forced to work with, while humiliating them with a magical mastery of his trade. His genius is so great that no one knows exactly what he`s up to (or who he`s really working for) except his almost equally brilliant lover-colleague, who assists him by covering up the murders, one of which is described in gruesome detail in the first few pages of the book. (The opening chapter is decidedly not recommended as bedtime reading.) Reeves-Stevens skilfully manipulates a plot based on bizarre love interests, a handy knowledge of physics, and a military-industrial complex conspiracy, in addition to convincing characterization and a cataclysmic, rapid-fire ending.