Mordum is a home movie shot by serial killers Peter Mountain, his sadomasochistic girlfriend Crusty and her depraved man-child brother, Maggot.

When Maggot is finished, he then lets a male captive out of another box, and he and Crusty force him to perform a penectomy on himself with a pair of cuticle scissors, then seal him back up.

Maggot and Peter then watch and masturbate to Crusty torturing two women, sexually abusing and repeatedly vomiting on them while a male corpse rots in the corner of the room.

Maggot disembowels one, chewing on her spilled innards and masturbating with them, while the other is beaten to death by Crusty and Peter, the latter dragging the body away to presumably have sex with it.

The trio are next shown playing in the snow, attending a concert, meeting up with friends, raping a woman, and going to a piercing shop, where Maggot receives a nose ring and gets into a fight with Peter over his relationship with Crusty.

The group then visit another serial killer, who shows them the contents of his shed; mutilated bodies, dying victims, and a headless and maggot-covered toddler, which Maggot eats a chunk of.