REVIEW: MARK OF CAIN An exciting, riveting, and cleverly-translated suspense thriller combined with police procedural, MARK OF CAIN carries the reader into the gritty underside of Cologne [Koln], Germany. This underside is hardly confined to the usual lawbreakers or common criminals. In one case, police had captured the man believed to be a vicious serial killer of prostitutes, and he was convicted and imprisoned. But that one was not the only danger. Unbeknownst to most of the police department, a detective has been culling a regular cut from the earnings of sex workers, and recently developed a violent streak of sadism, which he unleashes on the girls.