FBI Agent Thomas Mackelway (Aaron Eckhart) and Agent Fran Kulok (Carrie-Anne Moss) are put on the trail of Ben O'Ryan (Ben Kingsley), a serial killer who exclusively targets other serial killers. As the investigation proceeds, the agents begin to become aware of the possible existence of Suspect Zero, a mythical "super serial killer" responsible for hundreds of deaths across all 50 States who leaves no evidence behind to link his crimes together. The agents must decide if O'Ryan is the key that will allow them to catch Suspect Zero, or if he is Suspect Zero himself.