The Mole Man, out for revenge, lures the Fantastic Four to a deserted island. The Mole Man has constructed an elaborate tunnel system that can lower major cities of the world beneath the Earth's surface. The villain intends to eliminate the foursome so he can proceed with his plan.
Professor Gamma, a mad scientist mutated into a fish-man by the radioactive undersea rubble of what had been his base until it was destroyed by the Fantastic Four, seeks vengeance with his new-found powers as the Gamma Ray.
Galactus, a powerful being who devours planets for their energy, is coming to Earth. He is preceded by his herald, the Silver Surfer. The Watcher, another powerful being who is not allowed to take direct action, helps the Human Torch travel to Galactus's home base. Meanwhile, the FF convince the Surfer to take their side in the confrontation with Galactus. The FF fight Galactus to a standstill after the Torch brings the "ultimate nullifier" back from Galactus's home base. After Galactus departs, the Surfer also leaves to soar through the vastness of space. The episode...
A challenge from The Thing haters, The Yancy Street Gang, to the entire Fantastic Four turns out to be a forgery from The Red Ghost, who kidnaps the heroes to the moon for a revenge-fueled battle between the Four and him & his three super-powered apes.