On the Street Where You Die — Al Stevens

Stanley Bentworth is not all that tough. Previously a homicide cop, he drank his way out of a job and now runs a one-man private eye agency. When a wealthy financier needs an anonymous blackmailer found in a life and death situation, Stanley seizes the chance to earn a fee.
If he fails, the blackmailer outs his client to the mob, giving the client a one-way ticket to the landfill with Stanley an unwilling passenger on that ride.
He knows he must not fail, no small feat given that Stanley Bentworth is not all that tough.