Captured by the Mole Man, the Thing is blamed for the sudden blasts of heat that have been endangering the people of Subeterranea. As the Mole Man has his Moloids carry the Thing to a massive lava flow and his impending demise, the Fantastic Four's oldest foe explains what is going on in his realm. He reminds the Thing how he and the Fantastic Four last parted as allies after establishing his utopian society with his Outcasts,  but explains that recent a strange device from the surface appeared outside his domain and flooded the chamber with lava, apparently killing all the Outcasts in the process. The Thing explains that he is also trying to stop the schemes of one Alden Maas, a wealthy entertainment magnate who believes in the wild theory that if he super-heats the core of the Earth, he will cause the Earth to expand and grow in size and has kidnapped the Human Torch in order to achieve this goal. The Mole Man explains that such an idea is mad and that all Maas will achieve is causing the Earth's crust to split open, eradicating all life on the planet in the process. With both his domain and the surface world in danger, the Mole Man agrees to help the Thing to stop Alden Maas before it is too late.
Meanwhile, in New York City, Mister Fantastic departs from the Baxter Building in order to investigate a strange energy reading that the scanners in his lab has picked up. Taking the Fantasti-Car, Reed flies out to Sheep's Meadow in Central Park. Although his scanners have brought him to the source of the strange energy reading, Reed can find no trace of it, but fears that should it resurface again it could threaten the entire world.
At that very moment at the home that Reed and Sue share in Belle Porte, Connecticut under the guise of "Reed and Sue Benjamin", Franklin's babysitter Katie Dwyer returns with the boy after an outing. Their arrival coincides with Sue suddenly being racked with pain caused by her pregnancy. Recalling that nearly fatal trouble that she had while she was pregnant with Franklin, Sue hopes that this problem does not arise again. Needing to get Reed to check on her, Sue is suddenly surprised when the pain suddenly subsides. Putting on her "Sue Benjamin" wig, Sue then goes downstairs to greet Katie and see her son Franklin.
Back in California at the site of Project: Worldcore, Johnny Storm awakens from the last forced burst of flame that Alden Maas has forced him to carry on. After recollecting his situation, Johnny is visited by the female assistant of Alden Maas who is about to force Johnny to activate his powers again. Before she can throw the potentially fatal switch, Moloids suddenly rip through the floor and pull her underground. Out from the hole emerges the Mole Man and the Thing. After the Moloids pull Johnny from the machine that has been leaching his powers, he explains that Maas used a trap door to secretly kidnap Johnny during the race, and sending off a dummy car to crash in order to lead people to believe that he had died. With everyone on the same page, the Mole Man orders his Moloids to press forward on the attack to destroy Project: Worldcore. The group soon has to fight gun toting robots based on the various characters created by Alden Maas. Watching the developments from a control room as Alden and his assistants. Unwilling to allow himself to fail in his mission, Alden tells his men to prepare the thermonuclear device that he had prepared just in case.
Meanwhile, Johnny, Ben and the Mole Man fight their way to a massive door that is too thick for either Ben or Johnny to break through. The Mole Man has a solution, and summons his massive creature Giganto to smash through the wall. As Giganto begins to rip through the thick barricade keeping them out, Alden prepares to throw the switch that will set off the nuke that he hopes will generate the heat needed to support his theory. When Ben, Johnny and the Mole Man arrive, they arrive to find that Alden Maas is dead. One of his assistants explains that Alden suffered from a degenerative disease that affected his nervous system and spent repeated times in suspended animation. Revealing that they are robots, the aid explains that they were programed to follow the orders of Alden Maas and keep him happy. With their master dead, the robots then begin walking into the ocean to terminate their functions. With the danger over, Johnny and Ben thank the Mole Man for his help. Upset at his losses, the Mole Man warns the two members of the Fantastic Four that when next they meet it will not be as friends. After the Mole Man departs, Johnny and Ben leave in the Fantasti-Car headed for home.