Harry Angel, a down-and-out Brooklyn detective, is hired to track down a singer on an odyssey that will take him through the desperate streets of Harlem, the smoke-filled jazz clubs of New Orleans, and the swamps of Louisiana and its seedy underworld of voodoo.

Robert McCall is a former agent of a secret government agency who is now running his own private crime fighting operation where he fashions himself as "The Equalizer." It is a service for victims of the system who have exhausted all possible means of seeking justice and have nowhere to go. McCall promises to even out the odds for them.