The Choirboys, by Joseph Wambaugh:

In 1975, a police unit working the night watch in Los Angeles indulges in off-duty drunken hedonistic orgies. For them, the ‘choir practice’ sessions are a coping mechanism, a way to vent and let off steam to keep from exploding from the pressures of their job and the world around them. They work hard and play even harder, until caution is thrown to the wind one time too many, resulting in a tragedy that brings them all down.
These cops are not the ‘white nights in blue’ of so many clichéd TV shows. These are all-too human, with all the faults, weaknesses and character flaws they have to contend with as they fight both the criminals on the street and the bureaucratic hierarchy they work for and gripe about in private. This is one of the best police-themed novels in that it describes the effect police work has on the officers. Maybe once idealistic, these officers are now embittered and disillusioned and just struggle to make it through the day like everyone else.
Written by a seasoned former police officer, the characters and situations described throughout this novel have an authentic feel about them. By turns harrowing and hilarious, with characters you can both laugh with and loathe in equal measure, this remains one of the author’s best works.