 Four adventurers (Freda Kane, John Rennie, Walter Logan & Maria DeFalco) become trapped in Magnet Mountain s abandoned Castle of Satan. To escape the citadel s strange and terrible demonic attacks, they flee into a deep underground labyrinth. Here they discover a vast subterrainian kingdom peopled by bat-winged beasts & devils whose hierarchy is headed by King Satan (Vincent Weir) himself! To save their souls the adventurers must assist Satan s minions to infiltrate the mortal world above - but a clever stratagem foils the plan!