A mysterious object, resembling a meteor, crashes into Earth's atmosphere, unleashing cosmic energy that leads to chaotic weather patterns, power outages, and the formation of strange craters. In the midst of this crisis, the government seeks the expertise of Reed Richards to monitor the object's trajectory. At the same time, Reed and Susan Storm are preparing for their wedding, which is becoming a spectacle for the media. Just as the ceremony is set to commence, Reed's systems detect the approaching phenomenon threatening New York City.
Meanwhile, Johnny Storm discovers that the object is actually the Silver Surfer, a silver-skinned humanoid who rides a cosmic surfboard. Upon confronting the Surfer, Johnny finds himself overmatched and defeated. Later, when Susan checks on her brother, they unexpectedly switch powers; they revert back to normal upon touching again. Reed's investigation reveals that Johnny's recent encounter with the Surfer has altered his molecular structure, creating a unique ability to exchange powers with his team through physical contact.
As Reed traces the cosmic energy trail left by the Surfer, he uncovers a chilling truth: the planets previously visited by the Surfer have all been annihilated. Predicting that the next crater will open in London, the team rushes there but arrives too late to avert the disaster, resulting in the Thames draining into the newly formed crater. Their timely intervention saves the London Eye from collapsing.
In a twist of fate, the military compels the Fantastic Four to collaborate with Victor Von Doom, who has been freed from his petrified state thanks to the Surfer's energy. Realizing that the Surfer's board is key to his formidable powers, Reed devises a pulse generator designed to sever the Surfer from his board. In a fateful encounter in the Black Forest, the Surfer discloses to Susan that he isn't the true threat to Earth. As the military engages, they inadvertently provide the necessary distraction for the Fantastic Four to activate the pulse generator, effectively separating the Surfer from his board.
Captured by the military in Siberia and tortured for information, the Surfer's true allegiance is questioned by the team. Susan uses her powers to communicate with him, learning that he serves Galactus, a cosmic entity that must consume life-sustaining planets to exist. The Surfer's service to Galactus is a desperate attempt to preserve his own home planet, and he reveals that his surfboard acts as a beacon to lead Galactus to Earth.
In a calculated move, Doom seizes the board with a device he secretly crafted and escapes to China. The Fantastic Four mobilize, rescuing the Surfer and chasing down Doom in the Fantasticar. A dramatic showdown in Shanghai sees Doom impale Sue with a spear forged from cosmic energy. As the Surfer's powers wane, Johnny unifies the abilities of the team to mount a counterattack against Doom, successfully disabling his device while Ben Grimm employs a crane to send Doom plunging into the harbor.
As Galactus descends upon Earth, tragedy strikes when Sue falls lifeless in Reed's arms. Regaining his strength, the Surfer takes action, reviving Sue with the power of his board before joining forces with Johnny to confront Galactus. This culminates in a spectacular explosion of energy that engulfs Galactus within a cosmic rift, seemingly obliterating them both. Johnny, now immune to his previous ability to swap powers after a second encounter with the Surfer, returns to his unaltered state.
In the aftermath, Reed and Susan wed in Japan; however, an urgent alert interrupts their celebration as word comes that Venice is sinking into the ocean. With a shared sense of purpose, Sue hastily wraps up their wedding ceremony before the couple, along with Johnny and Ben, rush off to save the city.
In a mid-credits surprise, the Silver Surfer, thought to be lifeless, begins to stir in space as his board returns, signaling that he is very much alive.
