When a Superman and Batman appear one their world and claim that Skyscraper murdered Lois Lane, Superman kills Skyscraper and after the ensuing battle with the Maximums, escape via Boom tube.
With mysterious information provided by their fallen comrade, Bowman, the Maximums track Superman and Batman to their reality.
While Batman and Superman are fighting the Atomic Skull who is stealing a briefcase with radioactive materials in it from Wayne Tech, the Maximums appear, seeking revenge. The Soldier fires a bullet at the Skull, and it passes through Superman's hand and causing the Skull to violently release a large amount of radiation that Superman acts to contain. Although Robot observes Sueprman's heroic act, Viking will have none of it.
Soldier and Monster attempt to subdue Batman when Batzarro intervenes, blinding everyone with his "smoke" bombs. Batman's special batarang shocks Monster into breaking down into an inert monster and Becky, the little girl who merges with and controls him. As Superman crashes nearby, Batman leaps to take Becky to safety.
Viking using his axes, carved from black ice by Ymir, cutting Superman's skin, while Hornet flies into his ear and begins to grow... Viking strikes Superman down while Soldier kicks Batman into unconsciousness.
The Maximums return to their world via Boom Tube while Batzarro looks on.
Batman and Superman escape from a bizarre cell in the Maximums' reality. Back in new earth, Bizarro #1 and Batzarro somehow use the JLA transporter to attempt to reach Batman and Superman.
WHile battling Viking in San Franscisco, Superman is distracted by a woman being thrown from a bridge. Catching her, he realizes too late it's a set-up and is attacked by Robot, who no longer believes they murdered Skyscraper.
Meanwhile, Batman is wandering this reality's Alcatraz prison when he is attacked by an intelligent but feral Maximum, Wolfen and is defeated.
Bizarro ends up on a parallel earth, separated from Batzarro.
The Bowman visits Lex Luthor, who seems to know him. Bowman returns to the Maximums reality and releases the Kryptonite Man into an imprisoned Batman, possessing him.
The Kryptonite Man-possessed Batman fights with Superman while the Maximums argue over their fate. Superman uses Robot's exterior armor to encase K-Man and force him out of Batman's body.
Bizarro and Batzarro appear and try to drag their idols to safety, but Viking's axes cuts through Batzarro's chains, dropping him back to earth.
After Boom Tubing back to New earth, Bizarro appears on Paradise Island to recruit Supergirl's help in fighting the Maximums. Metron reminds Superman of his obligation to free Darkseid imprisoned in the Source wall.
It is revealed that The Joker and Mxy are playing a game with the heroes as game pieces. Mxy remarks that now that the pieces are all in place, the real game begins.
Superman frees Darkseid from the Source Wall.
Batman appears on a gender reversed earth and encounters Batwoman, Superwoman, and Superlad. Bizarro has somehow recruited various versions of Supergirl.
Everyone is eventually transported to a mysterious location that resembles a three ring circus. AFter killing Batzarro, The Joker reveals his plan to kill "every Batman there ever was or there ever will be."
It is revealed that the Joker and Mxy had create the Maximums and their reality as part of this game.
As everyone batlles one another, Mxy tricks Bizarro into activating a Phantom Zone projector on the Joker, freeing Bat-Mite who was apparently trapped inside him, empowering him. Mxy was unable to directly free his fellow 5th Dimensional imp, and had to have a creation of the Joker do it himself.
Mxy reveals to Darkseid his role in the coming crisis: "We ... have a future together that has yet to be revealed. "From the Fourth World ... into the Fifth Dimension." Kind like that ring tone, big D."