The Robinson party is planning a lift off from the planet that they are on, but an erupting volcano is interfering. Major West and Dr. Smith have been sent in the Chariot to cap the volcano using Hyper-Atomic explosive. As the eruption worsens, Professor Robinson orders them to turn back. Don and Smith are unable to turn back because they have been captured by primitive aliens. The aliens live in the shadow of the volcano. They are guided by a large computer called Protineus.