August Underground's Penance continues the series' narrative mode of showing the lives of serial killers (now just Peter, and his girlfriend Crusty) through their camera, though this installment abandons the "degraded footage" aspect employed by the first two films, being shot in high-definition.

After killing a man who breaks free of his restraints and tries to escape them, Peter and Crusty visit various locations in town and enjoy some fireworks at a celebration.

Next, Peter and Crusty go on a hike, assault a vagrant they find sleeping under a bridge, and cut a man open so they can pull his gurgling intestines out.

Peter bludgeons the father with a hammer and suffocates the mother, whom he is unsuccessful in trying to rape due to being unable to attain an erection.

Peter gets drunk and proceeds to take his frustrations out on a woman in the cellar while screaming insults at Crusty, who is still sobbing hysterically upstairs.

[4] The Worldwide Celluloid Massacre stated that while the leads "have to act in this installment" it was still "the same boring sickness" and "the same pointless realistic snuff trash".