It opens in a future where Batman’s dream has turned into a nightmare. Gotham is crime-free as is the rest of the world, which is ruled by “the iron fist of a man of steel.”
The bulk of the story is told through a flashback that explains how Superman goes from superhero to supervillain.
On the same day that Superman learns Lois Lane is pregnant, the Joker kidnaps her and kills Jimmy Olsen in the process. The Joker implants a trigger in Lois that will detonate a nuclear warhead in Metropolis upon her death. Then he exposes Superman to fear toxin that causes him to hallucinate his greatest enemy, Doomsday. Superman attacks and simultaneously kills his wife, unborn child and every man and women in Metropolis.
The best thing about this series is that we get to see Superman stop holding back. There’s a great moment when Green Lantern uses his ring to trap Superman and stop him from doing something he’ll regret. Superman effortlessly breaks free and then swipes his ring before he can use it again.
Meanwhile, the Joker breaks the fourth wall, as he often does. He explains his motive for going after Superman with video game terminology.
“Every time you and I play, I lose,” he tells Batman. “I was getting a bit bored of always losing. I thought I’d try this on easy mode for a bit.”
He’s sure that the death of his loved ones will push Superman over the edge. Sure enough, the blue boyscout bursts through the wall and punches a hole straight through the Joker, who laughs at being proven right. The real laughs start when Harley Quinn goes into hiding at the Arrow Cave, where she coaxes a Joker laugh out of Green Arrow for old times sake.
The Joker is a playable character so presumably he survives. Perhaps he gets some cybernetic enhancements. It would certainly explain how he goes toe to toe with powerhouses like Lex Luthor in his battlesuit and wins!