In a desperate attempt to get the advantage over the Legion of Doom before they awaken Perpetua, the Justice League had to bring one of the most dangerous beings in existence to the Hall of Justice: Mxyzptlyk. The 5th dimensional imp exists outside of time and space, so the League was willing to bet that he could help them find a way to end the threat posed by the Legion of Doom once and for all. He opened a door for them that led to the sixth dimension, and Superman volunteered to go by himself. Mere seconds after going through the door, an older Superman steps back into the Hall of Justice and tells the League that they won the war against Doom. However, as the Justice League follows this future Superman to his time, the reader sees something that rips all hope from them. In a black, empty void, there is Superman, trapped in nothingness.
(Spoilers Incoming)
The future Superman welcomes the Justice League into the House of Justice, showing them what will become of their hard work. As he states, the Hall of Justice became the House of Justice, despite the fact that it is more of a museum after their war with Doom. They then meet future versions of themselves, who tell them that rather than averting the war and the Multiverse falling out of place, they need to help the Multiverse move forward through existence and become something more. When Batman confesses his skepticism, Superman tells him that they can go over the details and plans tomorrow and that they should enjoy the world they helped create.
In the present, we see Batman chasing Deathstroke across a rooftop before Robin intervenes. However, this Robin that stops Slade isn’t Damian, it’s Jarro. This turns out to be nothing but a dream Jarro is having as Mera and Starman wake him up. As the two Leaguers that stayed behind to keep and eye on things, they noticed that Mxyzptlyk has grown an energy cocoon. As Jarro begins to read his mind, he discovers that Mxyzptlyk has made a deal with someone.
In the future, J’onn and Hawkgirl are shown the world by their married, future selves. They tell them that Mars was able to be repopulated after the war. In S.T.A.R. Labs, the future Flash and Green Lantern show their past selves their latest project: rebuilding the Multiverse from scratch. The future Wonder Woman shows her younger self the new Themyscira. After the war, the island was expanded and became the hub of knowledge in the world. Together with her New Amazons, including Vixen, Supergirl and Ivy, Wonder Woman helped create a universal language for all species. In Gotham, the city is bright and clean for the first time ever. The future Batman reveals himself to be Dick Grayson, who took up the cowl after Bruce sacrificed himself during the war. As a result of that sacrifice, Batman became the symbol of what humans could become and paved the way for the Justice League to win. But of course, this is Batman, so he has questions, starting with: “Where the hell are all the villains?” Elsewhere, J’onn and Hawkgirl discuss the world they helped create and how they end up together. During their conversation however, they are interrupted by their future child. He tells them that they need to flee, and that everything is not what it seems. In the present Hall of Justice, Mxyzptlyk grows to a giant size and attacks the Hall. It is revealed that Mxyzptlyk is in league with the Legion of Doom. Elsewhere, Superman is still trying to escape from wherever it is that he’s trapped. However, each time he tries to fly, he fails. He is then approached by the future Superman, who simply says, “So let’s talk, Clark.”
It seems the League is not in a wonderful future after all. If I had to guess, they’re trapped in a world Mxyzptlyk created for them. Why the imp is working with the Legion of Doom is the only part I don’t get, unless they used Perpetua to influence him. Either way, the League is in deep trouble with no sign of rescue in sight. Doom may be coming for them sooner than we expected.