Three FBI agents are guarding a key witness whose testimony will end the Chicago crime organisation. Led by Luigi Patrovita (Sam Wanamaker). When the witness and the bodyguards are brutally murdered in an early morning raid. FBI agent harry Shannon (Darren McGavin) seeks out the service of former agent Mark Kaminsky (Arnold Schwarzenegger). Kaminsky, forced to leave the Bureau due to his excessive violence and brutality, is asked to assume a second identity with the intention of infiltrating the Patrovita organisation and destroying it from the inside. Informed that the reward for a successful mission is reinstatement with the FBI, Kaminsky agrees to undertake the task.