Krona, an exiled
Oan, travels across the
multiverse and destroys universes seeking the truth of creation. When he arrives in the
Marvel Universe, the
Grandmaster — wanting to save his universe — proposes that they play a game. If Krona wins, the Grandmaster will lead him to
Galactus, a being in that universe who has witnessed creation. If he loses, Krona has to spare the Grandmaster's universe. Before choosing the players to participate in this game, Krona demands to swap champions, so the
Avengers (the Grandmaster's longtime adversaries) will represent Krona and the
Justice League (from Krona's home universe) will fight for the Grandmaster. The Grandmaster informs the Justice League that to save their universe, they have to gather 12 items of power — six from each universe — while his ally
Metron tells the Avengers that they have to do the same to prevent their world from being destroyed. The six items from the
DC Universe are the
Spear of Destiny, the Book of Eternity, the
Orb of Ra, the
Medusa Mask, the Bell, Jar and Wheel of the
Demons Three, and the
Green Lantern Power Battery of
Kyle Rayner. The six items from the Marvel Universe are the
Ultimate Nullifier, the
Evil Eye of Avalon, the
Wand of Watoomb, the
Casket of Ancient Winters, the
Cosmic Cube, and the
Infinity Gauntlet. The Justice League travels to the Marvel Universe and are shocked (especially
Superman) by the Avengers' failure to improve their Earth's condition; for example, the
Flash (Wally West) encounters a non-human-looking
mutant running from an anti-mutant mob and protects him. Convinced that the Flash is a member of
Magneto's
Acolytes, the mob attacks him as well. The Flash also discovers that the
Speed Force (the source of his powers) does not exist in the Marvel universe. When the Avengers visit the DC Universe, they are surprised by the "futuristic" architecture of its Earth's cities and the honors that the Justice League and other native heroes receive for their deeds. As a result, they (mainly
Captain America) become convinced that the Justice League are
fascists who demand that civilians hero-worship them. Various Justice League and Avengers members travel across the two universes and fight each other to retrieve the artifacts of power. A final battle for the Cosmic Cube takes place in the Marvel Universe's
Savage Land. After a climactic back-and-forth battle,
Quicksilver claims the Cosmic Cube. At that moment, Krona and the Grandmaster arrive on the scene, with the latter observing and commenting that the score is even at 6–6.
Batman and Captain America — who together investigated the cause of the contest and discovered its true nature and stakes — arrive. Captain America purposely throws his shield and knocks the Cube from Quicksilver's hands, allowing Batman to catch it. With Captain America's forfeiture of the Cosmic Cube, the Grandmaster announces the Justice League as the victors, with the final score being 7–5. Krona is unwilling to accept defeat, and attacks the Grandmaster, forcing the identity of Galactus from him. He then summons Galactus and tries to extract information about the origin of the universe. The Grandmaster uses the power of the artifacts and merges both universes together before Krona can tear Galactus apart. Reality is altered such that the Justice League and the Avengers are now longtime allies, regularly traveling between worlds to fight various threats. In addition, long-dead JLA members the
Flash (Barry Allen) and Green Lantern (
Hal Jordan) have reappeared. The universes, however, are incompatible with one another and begin destroying themselves and each other, with people switching between worlds. One side effect of this is that Superman and Captain America become paranoid, irritable, and short-tempered; their emotions flare to the point where they blame each other for everything that is happening. The appearance of a spectral Krona helps the heroes remember some of the contest and they find out what is happening to their worlds. The
Phantom Stranger appears to lead the heroes to the Grandmaster. Weakened by Krona's attack, the Grandmaster explains how he brought the universes together to imprison Krona using the 12 items, but Krona is merging the universes further to destroy them, hoping to create a new
Big Bang, which he can survive and finally learn its mysteries. Before dying, the Grandmaster asks the assembled heroes to stop Krona and restore order. At Captain America's insistence, he reveals various events that had taken place in the separate universes to show the heroes what sorts of worlds they are fighting for. Each team member witnesses the tragedies that had befallen them in their separate universes, such as the death of Barry Allen in
Crisis on Infinite Earths, Hal Jordan's descent into evil in
Emerald Twilight, and the loss of the
Vision and the
Scarlet Witch's children. Some of the heroes contemplate leaving the universes as they are to prevent the tragedies from happening, but Hal Jordan inspires everyone to work for the good of their worlds. Krona has trapped the universal avatars of
Eternity and
Kismet as reality continues to change. He has discovered that a sentience exists in universes and intends to force their spirits out, giving him their secrets. Both teams of heroes reconcile their differences with one another and make plans to stop Krona. Invading Krona's inter-dimensional base, Captain America leads every hero who has been a member of the Justice League or the Avengers. Chronal chaos at the base causes an ever-shifting roster of heroes to confront every villain whom the teams have ever fought with the villains having been mentally enthralled by Krona. Even though the chaos and the sheer forces against them (both from Krona and the summoned villains) cause the heroes to fall one by one along the way, Krona is ultimately defeated when the Flash distracts him long enough for
Hawkeye to shoot an explosive arrow into the machine he used to keep both worlds merged, after which the Flash takes the items of power — both heroes having been earlier presumed dead in battle. Krona is then sucked into the forming vortex. The Earths are separated with help from the
Spectre (who at this time is Hal Jordan, now restored to his current state) and the universes are returned to their normal states. As the heroes from both universes return to their proper places, they affirm that whether they do too little or too much, they are still heroes who will always fight the good fight. Krona has imploded to form a
cosmic egg, which is stored in the
Justice League Watchtower; Metron states that when the egg hatches, Krona will learn the secrets of its universe's creation by being part of it. Metron and the newly resurrected Grandmaster discuss how Metron intentionally lured Krona to the Marvel Universe. The Grandmaster says that this is the first game that he has ever played in which all sides won (the Grandmaster by way of the battle between the Justice Leaguers and Avengers, the heroes by saving their universes, and Krona by eventually gaining the answers that he sought). == In other media ==