In 1964 on Earth-828, the Fantastic Four are celebrated as heroes after gaining powers from cosmic rays. Reed Richards’ inventions advance technology, and Sue Storm’s diplomacy promotes global peace. When Reed and Sue announce they are expecting a child, the world wonders if the baby will inherit powers.
Their lives are disrupted when the Silver Surfer warns that Earth is marked for destruction by Galactus, a cosmic being who devours planets. The team confronts Galactus, who demands Reed and Sue’s unborn child, Franklin, to cure his eternal hunger. They refuse, escape, and Franklin is born.
Back on Earth, the public debates sacrificing Franklin to Galactus. As protests grow, Reed develops a plan to teleport Earth to safety, while Sue rallies nations to cooperate. The Silver Surfer, revealed as Shalla-Bal, struggles with her guilt but initially refuses to help.
In the final battle, Galactus captures Franklin but is forced into a teleportation portal with Shalla-Bal’s help. Sue dies pushing him through but is revived by Franklin. The team survives to fight another day, though the world remains wary.
A mid-credits scene reveals Franklin meeting a mysterious figure in a green cloak holding a metal mask.