On a Caribbean island June has inherited, the Challengers rescue an alien creature and name it Cosmo. An active volcano on the island splits the team. When Prof and Red are almost killed, they find that the volcano is man-made and are trapped by a steel cage. Meanwhile, Ace, Rocky, and June are snared in a steel net. Cosmo chews through the steel and projects eye-beams that disintegrate foliage as they hunt for Prof and Red, who had been captured by thugs. Cosmo's paws project force-beams to disarm the thugs -- who had been using the island as a weapons depot -- so the Challs can subdue them.
The Challengers are transported by Dr. Oren Gough to the future where the Cosmic Creatures are attacking. Gough explains that the people of Earth will be evacuated, then a volti-ray used to wipe out the creatures. The Challengers volunteer to give their lives by manning the ray, but a man named Lenroy and his friends are also given the privilege. That night, the Challs discover that Lenroy -- who has secretly made the ray harmless to humans -- actually plans to use this opportunity to take over Earth. The Challs fire the volti-rays to destroy the creatures, subdue Lenroy, and return home.