An experimental submarine, the “Siren II”, with a very experienced crew is sent to find out what happened to the “Siren I” after it mysteriously dissapeared in a submarine rift. Things go awry when they begin to find things that shouldn’t be there…

People are dying mysteriously and gruesomely, and nobody has a clue what the cause is. Only health worker Mike Brady has a possible solution, but his theory of killer slugs is laughed at by the authorities. Only when the body count begins to rise and a slug expert from England begins snooping around does it begin to look like Mike had the right idea after all.

History Professor Brad Fletcher heads west for his health, but falls in with Soloman Bennett’s outlaw gang. Fascinated by their way of life, Fletcher finally takes over the gang, leading with a new ‘efficient’ ruthlessness.