From Amazon.co.uk:
Harry Barnett is a middle-aged failure, leading a shabby existence in the shadow of a past disgrace, reduced to caretaking a friend's villa on the island of Rhodes and working in a bar to earn his keep. Then a guest at the villa - a young woman he had instantly and innocently warmed to - disappears on a mountain peak.

Under suspicion of her murder, Harry stumbles on a set of photographs taken by Heather Mallender in the weeks before her disappearance. Desperately, obsessed by the mystery that has changed his life, he begins to trace back the movements and encounters that led to the moment when she vanished into the blue. The trail leads him back to England, to a world he thought he had left for ever, and at every step of the way a new and baffling light is shed on all the assumptions that have made Harry what he is.

Left at the book exchange stand near Factorie and Converse on level 3.

Release #17 for the 2019 Sapphire Challenge.
Release #30 for the 2019 Movie Books Challenge.