The Drop - Michael Connelly

Harry Bosch is facing the end of the line. He's been put on the DROP - Deferred Retirement Option Plan - and given three years before his retirement is enforced. Seeing the end of the mission coming, he's anxious for cases. He doesn't have to wait long. First a cold case gets a DNA hit for a rape and murder which points the finger at a 29-year-old convicted rapist who was only eight at the time of the murder. Then a city councilman's son is found dead - fallen or pushed from a hotel window - and he insists on Bosch taking the case despite the two men's history of enmity.

The cases seem to be unrelated; one leads to the discovery of a killer operating in the city for as many as three decades, the other to a deep political conspiracy that reached back into the dark history of the police department...