Frank Bullitt is selected by Chalmers, a politician with ambition, to guard a Mafia informant. Bullitt's friend is shot and the witness is left at death's door by two hit men who seem to know exactly where the the witness was hiding. Bullitt begins a search for both the killer and the leak, but he must keep the witness alive long enough to make sure the killers return. Chalmers has no interest in the injured policeman or the killers, only in the hearings that will catapult him into the public eye and wants to shut down Bullitt's investigation.