Desperate for money to buy food, Jason, Pythagoras and Hercules take jobs as rat-catchers but are soon sacked when they start eating the food they are supposed to be guarding.

Meanwhile, after consuming a joint of meat he has stolen from a strange house full of skulls and statues, Jason realises something strange is happening to him when he wakes up naked in an animal pen. It turns out that he has been cursed after eating a sacrificial offering to the goddess of witchcraft, and by night he is transformed into a werewolf-type creature that goes out to hunt in the streets of Atlantis.

Pythagoras discovers a remedy that requires silver, and approaches Ariadne for help. With the garrison closing in on the nocturnal predator, Hercules and Pythagoras track Jason down in the nick of time and administer the cure.