The tale begins with Emperor Ming the Merciless declaring his intent to wreak havoc on Earth through a series of catastrophic disasters, including earthquakes, hurricanes, volcanic eruptions, tornadoes, and even something he ominously terms as "hot hail." In the midst of this chaos, Flash Gordon (Sam J. Jones), a star player for the New York Jets, boards a small plane where he encounters a determined travel journalist, Dale Arden (Melody Anderson). Their flight takes a perilous turn when a meteorite sent by Ming strikes the cockpit, causing the pilots to be ejected from the plane. Flash, in a show of heroism, manages to take control and crash-lands in a greenhouse owned by Dr. Hans Zarkov.
Zarkov has long suspected that the disasters plaguing Earth are the result of extraterrestrial interference, specifically from the planet Mongo, which he believes is sending its moon on a collision course with Earth. He has constructed a secret rocket ship to investigate these phenomena but finds his assistant unwilling to assist him. Instead, he cleverly lures Flash and Dale aboard the rocket, leading to an unexpected launch that transports the trio through a vortex to Mongo, where they are promptly taken captive by Ming.
Upon arriving at the palace, Ming gives orders for Dale to be prepared for his own pleasure, while Flash attempts to resist, only to be subdued by Ming's guards. In a twist of fate, Ming orders that Zarkov undergo a process of reconditioning and plans to execute Flash using lethal gas. However, Ming’s daughter, Princess Aura (played by Ornella Muti), conspires to save Flash, who she is drawn to. She secures the intervention of Ming's Chief Surgeon, who administers an immunity serum, enabling Flash to escape the palace.
Meanwhile, Zarkov appears brainwashed under the control of Klytus (portrayed by Peter Wyngarde), who is Ming's right-hand man and enforcer. As Aura and Flash make their escape in a shuttle, they journey to Arboria, the kingdom ruled by Prince Barin (Timothy Dalton), Aura's lover. Along the way, Aura teaches Flash how to use a telepathic communicator, allowing him to contact Dale and reassure her of his survival. Dale, locked in Ming's chambers, resolves to escape once she learns that Flash is alive.
As Zarkov and Dale navigate their own challenges, they encounter Prince Vultan (Brian Blessed) and his Hawkmen, leading to a series of action-packed escapades. In a landscape fraught with distrust, Barin finds himself countering Flash, who must prove himself worthy in a deadly ritual. Barin, grappling with his feelings for Aura, eventually joins forces with Flash when they confront a common enemy: Klytus. Together, they manage to outwit and overpower Klytus, setting the stage for a climactic battle against Ming.
With tensions mounting, Ming, in a fit of rage, orders the destruction of Vultan's Sky City, prompting Flash to pull off a daring escape on a rocket cycle. He rallies his allies, including the Hawkmen, to plot their collective retaliation against Ming's forces. In a final showdown, they launch a daring attack on Ming's kingdom, where Flash’s bravery shines amidst chaos.
The stakes escalate as Flash offers Ming a chance at mercy in exchange for ceasing his onslaught against Earth, a proposition Ming vehemently rejects. As the impending doom of Ming's power looms, Flash confronts him one last time, leading to a cataclysmic conclusion.
As peace seems to dawn upon Mongo, a celebratory atmosphere ensues with the victory over Ming. Barin is heralded as the new ruler while Flash, Dale, and Zarkov contemplate their future on Mongo, since the portal to Earth has been severed with Ming's defeat. With their fates intertwined, they agree to stay, while Zarkov devises a plan to return them home.
The screen fades as the final image highlights Ming's empty power ring, which an unknown figure picks up, leaving audiences to ponder the continuity of this saga, capped off with an echo of Ming's sinister laughter lingering in the air.
