A long time ago when the earth was green, the inhabitants of an ancient Greek island used to sacrifice virgins to placate a beast that lived in an underwater cave.
While a modern achaeologist (James Earl Jones) and his girlfriend (Lydia Cornell) are raiding the cave of its treasures unbeknowst to the island's inhabitants, another man and his sister (Martin Kove and Mary Louise Weller) are searching for their other sister who they believe might have travelled here. The natives aren't thrilled with outsiders visiting the island and are warned off by an elder played by José Ferrer. It turns out the lost sister is on the island, but she is plagued by strange dreams. Jones, in his raids on the cave, has re-awakened the beast, and it kills his girlfriend. The villagers realize another sacrifice will have be made, and luckily the lost sister just happens to be a virgin.
This is a moderately competent cheap monster movie. We hardly ever see the monster, and for a movie that involves an island and an underwater cave, we hardly ever go underwater, either. Ferrer and Jones manage to raise the level of the proceedings enough to make it only just marginally entertaining. Let's face it: James Earl Jones could read the dictionary with so much gravitas that you'd think the world was going to end before he gets past "ablate."
There's a lot of talent on display here -- Ferrer and Jones have four Oscar nominations and a win between them -- but this movie seems to have been a career killer. It took director Richard Jeffries 26 years to get his next film made, and Weller pretty much retired after this. On the other hand, Lydia Cornell was just starting her career -- she was just about to breakout big on the tv sitcom Too Close for Comfort -- and although she still acts occasionally, she's gone on to a career as a progressive radio host in Las Vegas and an active blogger.