The mystery elements in Deep Waters are enough to power the plot, and include a few red herrings to keep the reader on their toes, but they have to share the stage. Inspector Ikmen's own Albanian heritage, and revelations about his mother's death when he was a child, make the case unusually personal. And one of his subordinates is courting a psychiatrist involved in the case. (There's a bit of psychiatric theory thrown in as well, presumably drawing on Nadel's own work in mental health.)
The characters all seem a little like types: Ikmen himself is incorruptible, his long-suffering wife is a devout Muslim and one of his cousins is a transsexual, and his subordinates include a scion of the Ottoman minor aristocracy, a Yazidi, a modernist intellectual, and so forth. If Deep Waters is hardly high literature, however, it's easy reading and conveys a feel for its Istanbul setting — which made it a good choice as reading material for a trip to Turkey.