The Forgotten Man by Robert Crais

Six months after nearly losing everything to the men who kidnapped his girlfriend's ten-year-old son, Elvis Cole is slowly coming back to life - when he receives an ominous phone call from the LAPD. An unidentified body has been found in a seedy Los Angeles alley. The only clue the cops have is a packet of newspaper articles about the past exploits of Elvis Cole - and the fact that before the man died, he said he was Elvis's father...Joe Pike is the only person who can help Elvis navigate his past. As they investigate, Elvis is haunted by the fact that, at last, he might have found his father. But with each clue they uncover, a troubling picture emerges about the dead man. And as Elvis and Joe approach his true identity, they unwittingly walk straight into a hornet's nest.