The Falls by Ian Rankin

A missing student, a six inch coffin containing a wooden doll, and mysterious role-playing games on the Internet are the intriguing elements of the latest case to challenge Inspector Rebus. The missing student comes from an influential family, and Rebus begins to get a bad feeling about the case in Warsaw. Whilst Rebus follows up a link with the distant past, his DC, Siobhan Clarke tackles the Internet challenges set by the mysterious Quizmaster.