Spook: a "nameless detective" novel

Shaken after a hair's-breadth escape from death, Nameless has made changes in his professional life, but he's not put himself out to pasture. Again he enters San Francisco's shadowy underworld, this time in a search for the identity of a gentle, mentally disturbed homeless man who has been found dead in an alley doorway. Clues are few, but Pronzini, working at the top of his form, takes his seasoned private-eye hero to a new phase of a still-evolving thirty-year career.