This film is based on the novel Ratman's Notebooks, by Stephen Gilbert. Bruce Davison is Willard Stiles, a 27-year-old mama's boy whose repressions are bottled up inside and come to the fore in his nervous nail-biting. As one character describes Willard, "Willard is basically an extrovert, but it's all inside." Willard and his possessive invalid mother, Henrietta (Elsa Lanchester), live in thrall to Al Martin (Ernest Borgnine), the man who took over a foundry business after the death of Willard's father. Willard inwardly seethes but mostly stays in his run-down mansion with his mother, making friends with the rats that infest the place -- he even names them, Ben and Socrates. However, when Henrietta dies, things change. Al, in a rage, kills one of Willard's pet rats. Not only that, but Al also fires Willard from his job at the foundry. Losing his patience, Willard meets with his rat friends to exact his revenge for a lifetime of humiliation and neurosis.