Scarab

The city of Soshambe on the planet Tashista has been tormented by a serial killer nicknamed Scarab who strikes during the same season each year. Tashista employs an economically determined caste system and since Scarab's victims have all been from the bottom of the social order, there has been little serious effort made to identify or capture him. When the son of a prominent citizen becomes the latest victim, the authorities enlist the aid of Sandor Dyle, an offworlder and amateur detective, who uses pattern analysis to solve crimes.