At the start of this issue, the Human Torch rushes to the Fantastic Four, as no one answered his signal, only to find the team shrunk down to a tiny size. The team soon grows to full size, although none of them have any explanation for why it happened. As they're pondering what happened, a voice from nowhere says that they're helpless before him, and that this is only the beginning. All of them reveal that they also shrunk down a few days ago, but didn't say anything because it would have sounded ridiculous. Mr. Fantastic decides that the superhero Ant-Man may have an explanation for why they're shrinking down, but the rest of the team is sceptical that he even exists, or that they need his help. An ant by Mr. Fantastic's feet hears this, and a signal is by ants to Hank Pym's lab, where he changes to Ant-Man and travels to the Baxter Building. He asks them what their problem is, and after it's explained, Ant-Man gives Mr. Fantastic two drops of fluid, one which will cause them to shrink, and the other which will cause them to grow in size.
The next day, the Thing and Mr. Fantastic are at Alicia Masters' house testing a new serum to turn the Thing to his human form when a voice coming from nowhere, just like earlier, is heard. However, this one warns the two members of the Fantastic Four of Doctor Doom, and tries to tell them what he's planning, but is cut off. The same voice is heard by the Human Torch and the Invisible Woman, and when the team regroups, they all take some of Ant-Man's formula and shrink down to a tiny size. When they finish shrinking, they find themselves in a whole other world, where they find Doctor Doom. Doctor Doom shrinks the Fantastic Four down once more so they won't attack him, and then explains that after they last saw him (in Fantastic Four #10), he found himself in this world. His science was more advanced than the people's who lived here, so he overthrew the king and his daughter, Princess Pearla, before shrinking down the Fantastic Four from afar and toying with them.
The Fantastic Four are then knocked out and placed in an underwater prison with Princess Pearla, who explains that the "water" outside is really acid. She also says that she was the one who tried to warn them of Doctor Doom, because he is planning on selling them as slaves to the warriors of the planet Tok. Meanwhile, in the normal world, Ant-Man finds the Fantastic Four missing, so shrinks himself down to find them. Unfortunately, he's captured by Doctor Doom. Back at their prison, the Fantastic Four manage to escape through the acid by forming a capsule of their prison walls and floating it to the surface. The Fantastic Four then regrow themselves to normal size using Doctor Doom's machine, before freeing Ant-Man. However, in the confusion, Doctor Doom grows and returns to the normal world. After fighting off Doom's former guards and stopping the warriors from Tok, the Fantastic Four also return to the normal world to find and stop Doctor Doom.