A crazy old woman steals what looks like all-butter shortbread from three statues wearing red hats. This causes an earthquake which releases ancient demon spores from a cave into a nearby pool of water. Unfortunately, this pool is precisely where a lesbian professor—part of a group of students and teachers who are spending a few days camping in the woods—decides to refill her water canteen. She accidentally ingests the spores, which causes the eruption of huge, thrashing, veiny, slime-covered tentacles that seek out new victims and enter the nearest orifice, thus allowing the demon to pass from host to host.

Manami, the sole survivor of Angel of Darkness 2, is rushed to hospital where she slips into a deep sleep. A priest correctly suspects that the demon (now referred to as an Injuu) is inside Manami's body, but by the time he is able to confirm his theory, the creature has already moved on. As before, the tentacled beastie passes from host to host (by thrusting its slimy appendages into its victims' orifices), eventually ending up inside goody-goody schoolgirl Fumie, who does her best 'Linda Blair' impersonation for a while, before the priest inevitably turns up to save the day.