Tim Kearney, a San Quentin prisoner with an "impulse control" problem, expects to spend the rest of his life in jail, until the FBI makes him an offer he can't refuse: he can go free if he agrees to assume the identity of the late drug lord, Bobby Z, so the Feds can deliver him to a Mexican kingpin in exchange for a kidnapped agent. Tim happily agrees to the charade, but when the plan backfires, Tim finds himself at the top of the DEA's most wanted list and a target of some old enemies.