Lionel Essrog (Edward Norton), a lonely private detective living with Tourette Syndrome, ventures to solve the murder of his mentor and only friend, Frank Minna (Bruce Willis). Armed only with a few clues and the engine of his obsessive mind, Lionel unravels closely guarded secrets that hold the fate of New York in the balance. In a mystery that carries him from gin-soaked jazz clubs in Harlem to the hard-edged slums of Brooklyn and, finally, into the gilded halls of New York's power brokers, Lionel contends with thugs, corruption and the most dangerous man in the city to honor his friend and save the woman who might be his own salvation.