A Stab in the Dark, by Lawrence Block

This is yet another early Matthew Scudder novel; it’s interesting mostly
in that this is the book where Scudder first begins to admit to himself
that he has a drinking problem. He has a couple of blackouts, and does
some seriously dangerous and stupid things, and almost–but not quite–
persuades himself to go to an AA meeting. The mystery itself serves
mostly as background for Scudder’s own story in this one.