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.

A caretaker at a summer camp is burned when a prank goes tragically wrong. After several years of intensive treatment at hospital, he is released back into society, albeit missing some social skills. What follows is a bloody killing spree with the caretaker making his way back to his old stomping ground to confront one of the youths that accidently burned him.