Operating an unstoppable robot tank, Lex Luthor robs a bank. Returning from France, Superman drops Lois Lane off, on the roof of the Galaxy Broadcasting building, before engaging Luthor. Superman hurls the rooftop Daily Planet globe at the tank, destroying it, then turns Luthor over to the authorities. Afterwards, Superman and Lane discuss their relationship. Lane is frustrated that Superman's "jobs" constantly come between them. On Earth-2, Alexei Luthor targets the Daily Star building for destruction, via an orbital missile platform, in a ploy to slaughter Superman's friends. After being rebuffed by the initial missile launch, Superman catches one of the missiles, and hurls it into the barrage, detonating them all. Tracking the launch signal back to Luthor's lair, Supeman takes the villain down, before handing him off to the authorities.
Prepared for just such a contingency, Lex Luthor uses technology, secreted on the person of a fellow inmate months ago, to bridge the dimensional gap between Earth-1 and Earth-2. Acting quickly, he exchanges places with his Earth-2 counterpart. As the two Luthor's possess physical distinctions that set them apart from one another, they are released from their respective prisons. Alexei Luthor draws the Superman of Earth-1 to him, by detonating explosives under the streets of Metropolis. As soon as Superman comes after him, Luthor ensnares the Man of Steel with strength-draining gravity bands that carry him into orbit. On Earth-2, Clark Kent is sharing an amorous moment with his wife, Lois Lane, when his super-hearing alerts him to a little girl about to be run over in the street.
Kent, as Superman rescues the girl, who turns on him, shooting him with a weapon that rapidly shrinks him to microscopic size. Watching from the Daily Star building, Lane races down to assist. After knocking Lex Luthor down, Lane recovers the little girl's gun, and reverses it's effects. Superman regains his normal stature, knocking Luthor out as he grows. On Earth-1, Superman is being drawn into a black hole. The gravitational forces of the stellar phenomenon, though, disable the gravity bands, freeing the Man of Steel. Returning to Earth, Superman takes out Alexei Luthor, with his super-breath, before Luthor can murder Lane. Traveling to his Fortress of Solitude, Superman confers with his Earth-2 counterpart on what to do about the two Luthors. The Supermen decide to hurl the Luthors into inter-dimensional space.
Lex Luthor, though, has an escape contingency for that as well. Using the dimension bridging capabilities of his armor, Luthor, and his counterpart, escape to Earth-3. There they encounter the Supermen's evil counterpart, Ultraman. Lex Luthor strikes a bargain with Ultraman, offering to deliver Earth-3 to Ultraman, in exchange for Ultraman's help in killing the Supermen. Unbeknownst to the villains, they are observed by Lois Lane's Earth-3 counterpart. Alexie Luthor has his own plans for dealing with the Supermen. Luthor has Ultraman assemble an ion tractor beam, so that he can pull Earth-1 and Earth-2 into the same dimensional space, destroying them both. Lex Luthor is horrified at the scope of his more bloodthirsty counterpart's plan. Lane meets with the Luthor's counterpart on Earth-3, Alexander Luthor.
Unlike his counterparts, Alexander Luthor is a good man. One whom Lane convinces to become Earth-3's first super-hero. Luthor contacts the Supermen, who are both on Earth-2, and begs them for assistance. Bridging the dimensional gap between Earth-2 and Earth-3, the Supermen meet with Luthor and Lane. Donning a suit of powered armor, Luthor accompanies the Supermen to confront Ultraman and the Luthors. Lex Luthor pleads with Alexei Luthor to reconsider his plan for destroying their worlds. Fueled by Kryptonite, Ultraman intercepts the Supermen before they reach the Luthors' lair. Ultraman quickly defeats both Supermen, then topples the skeleton of a skyscraper over top of them. Engaging with Alexander Luthor, Ultraman suddenly finds himself rendered intangible.
While Luthor finsihes up with Ultraman, the recovered Supermen continue on to the Luthors. Faced with the threat of returning to prison, Lex Luthor signs off on Alexei Luthor's worlds destroying scheme. The Superman of Earth-1, using technology borrowed from Alexander Luthor, heads off into inter-dimensional space to prevent Earth-1 and Earth-2 from colliding. The Superman of Earth-2 remains behind to deal with the Luthors. Despite the intense pain their weapons cause him, Superman musters the fortitude to destroy the ion tractor beam. In inter-dimensional space, Superman uses Alexander Luthor's "phantom ray" to turn the two Earths intangible, so that they pass harmlessly through one another. The weapon, though, is not capable of doing the job without greater power.
Superman harnesses the power of the ion tractor beam itself to increase the "phantom ray's" capability. The two Earths become intangible, allowing them to safely occupy the same dimensional space, for the few moments it takes for them to pass through one another. Using the Luthor's devices to place the two Earths back in their proper vibrational plane, the Supermen carry their respective Luthors back to their respective Earths, and back to prison. Alexander Luthor, having defeated Ultraman, vows to continue to fight for justice on Earth-3. On Earth-2, Superman has a happy reunion with his wife, Lane. On Earth-1, Superman's relationship with Lane seems to drift further apart.