The Identity Man by Andrew Klavan
A nationwide manhunt is underway for John Shannon, a petty criminal framed for murder. But he's convinced he won't get caught. He's hiding in the ruins of a city destroyed by a terrible flood, and, thanks to a mysterious foreigner calling himself the Identity Man, he has a new face, new papers, and a new life. But the city is crawling with corruption. Crooked politicians, gangsters and dirty cops are everywhere, and for some reason Shannon doesn't understand, all of them want him dead. John Shannon has run out of second chances, and now he's running out of time. Moving through the darkness in the burnt-out shambles of a dirty town, he must ferret out the secret of his new life, before he is left with no life at all.