This film is also known as The Fear Chamber, and I hadn't seen this film in years. I know many people dislike this film, but I find it to be a pretty good little sci-fi film.
Karloff is Dr. Karl Mantell whose assistants find a living rock under a volcano and bring it back to the lab.
it's discovered that the being lives off of certain human hormones that can only be brought about by fear. Unbeknownst to Mantell his assistants set up a torture chamber and kidnap women to torture and bring about the fear, thus get the hormones.
The evil is finally uncovered and stopped, and yes, there are several gaping plot holes but you really have to put your mind on hold for these types of films.
The rest of the cast includes Julissa, Carlos East, Isela Vega and the unforgettable Yerye Beirute.
This was the final film Karloff appeared in as it was the last he shot scenes for.