Watching the Dark (Inspector Banks)

DCI Alan Banks is back - and this time he's investigating the murder of one of his own.
A respected officer convalescing at the St. Peter's Police Treatment Centre, DI Bill Quinn, is killed by a crossbow while on the facility's tranquil grounds, and the initial investigation uncovers compromising photos in his room. Soon after, Professional Standards Inspector Joanna Passero arrives in Eastvale and insists on working the case alongside a reluctant Banks, who's convinced a police officer shouldn't be deemed guilty without proper evidence.
But the more they learn, the more likely it seems that Quinn wasn't all he was reputed to be, that his murder is linked to another vicious crime in Yorkshire and to a cold case - the disappearance of a nineteen-year-old English girl, Rachel Hewitt, in Estonia six years earlier.
Intricate, engrossing, and psychologically tense, the twentieth book in the internationally bestselling series by award-winning author Peter Robinson may be the most suspenseful Banks mystery yet.