This is set in a retro-futuristic 1960s where Reed Richards, Sue Storm, Johnny Storm, and Ben Grimm are celebrities—the world's first superheroes, flying in their Fantasti-Car, operating from the Baxter Building. They're four years into their fame when Sue discovers she's pregnant.
The film opens with optimism. They're planning for a future where Franklin Richards will grow up in a world protected by his parents. Then the sky opens and Galactus arrives.
He's not a villain in the traditional sense. He's a force of nature, older than galaxies, cursed with an eternal hunger that can only be satisfied by consuming the life energy of entire planets. He's not evil—he's necessity given form, and he's come to Earth because he senses something unprecedented: the unborn child carries cosmic potential that could end his hunger forever.
Galactus makes an offer. Give him the child, and Earth lives. Refuse, and he consumes the planet as he has consumed thousands before. It's not a threat. It's a fact.
Reed and Sue refuse. No negotiation. No debate. Their child is not a bargaining chip. The Fantastic Four, along with Earth's militaries, attempt to fight a god. It's hopeless. Galactus is incomprehensibly powerful. Johnny's flames are nothing. Ben's strength breaks against him. Reed's intellect can't find a solution fast enough. Sue is pregnant and fighting to protect her child against something that views planets as food.
Galactus forces Sue into labor. It's an act of cosmic violence—using his power to accelerate the birth so he can claim Franklin immediately. The child is born aboard their spacecraft while Galactus waits below.
Franklin Richards is born with power that manifests immediately. He's a reality warper, a being who can reshape existence itself. Reed realizes that Galactus was right—Franklin could feed him forever. But Franklin could also do something else.
Sue sacrifices herself, channeling all her power into pushing Galactus through a dimensional vortex that Franklin creates. It's a mother protecting her child with her life. She succeeds. Galactus is gone. Sue is dead.
Then Franklin, with powers he shouldn't understand, brings his mother back. Reality rewrites. Sue gasps back to life, and the impossible has become possible. Franklin is perhaps the most powerful being in the universe, and he's a baby.
The film ends with Reed announcing to the world that Galactus demanded their son, and they refused even when it meant Earth's destruction. They won, but the cost was almost everything.
The mid-credits scene shows Sue recovering when a man in a green cloak approaches, his face hidden behind a metal mask. "Your son will reshape everything," he says. Doctor Doom has arrived, and he sees Franklin Richards as either the salvation or damnation of reality itself.
The Fantastic Four: First Steps is about the impossibility of parenthood when gods demand your child. It examines whether any life—even billions—is worth more than your child's life, and concludes that for Reed and Sue, nothing is. The film sets up Franklin as a wildcard for the MCU's future, a being whose very existence destabilizes cosmic hierarchies. Galactus may return. Doom is watching. And the Fantastic Four just became the most important family in existence.