Holland (Charles Bronson) is a retired CIA special agent. Moloch is a doctor who uses his medical knowledge to be the best torturer for South American dictators. When Moloch tortures and kills his friend, Holland comes out of retirement to get Moloch. His dead friend's widow comes along so Holland can pose as a man on vacation with his wife in Guatemala.
Holland kills Moloch's guards one by one, to rattle Moloch and make him know someone is coming for him. Holland captures Moloch's sister to draw Moloch out. Moloch sends his thugs for her, and in the shootout the sister is killed. They still set up a meeting for Moloch to ransom his sister.
At the meeting, Moloch has the friends daughter hostage. He threatens to kill her, if his sister is not returned. With the sister dead, it looks bad. The local villagers recognize Moloch as the guy who has tortured and killed their relatives. They take matters into their own hands, beating Moloch to death.
The final scene shows the friend's widow and daughter with Holland in his island retirement.
Thanks Joseph C!