A small exploratory vessel crashes onto an unknown ocean planet after its crew is seized by a sudden madness. After escaping their sinking ship, the five survivors are helped to the surface by giant squid-like creatures who guide them to what appears to be the planet's only island. To their surprise, they are greeted on the shore by primitive humans, who prove to be welcoming despite their cannibalistic rituals. But their fixed smiles and total docility suggest that something more sinister...