I guess that's not technically true. I understood what I already knew about this event: Brainiac has kidnapped cities from planets throughout the multiverse. Beyond that, I've got nothing.
I'll start at the beginning. Superman narrates that Brainiac has infected him with the Doomsday virus and, for reasons that we never learn, he pulled Brainiac into a black hole to save Metropolis. (I'm assuming that he's describing the events of "Superman: Doomed.") He's then confronted by a cosmic-sized version of Brainiac announcing that all other versions of Brainiac are (unknowingly) part of him. He announces that he sent the version of Brainiac that Superman had been fighting to break his resolve or die trying (though, we don't learn why Cosmic Brainiac wanted to break Superman's resolve). Superman asks Cosmic Brainiac if he killed this other Brainiac, but Cosmic Brainiac announces that Superman did. (Despite Superman's shock, we also never confirm this assertion or learn how it happened.)
At this point, it seems like we're missing a page or two. Suddenly, we skip from Cosmic Brainiac and Superman having this conversation while floating in space to Superman chained to some sort of machine that might actually be inside Cosmic Brainiac. We learn that Cosmic Brainiac is experimenting on him because, despite his cosmic insignificance, he's a threat to Cosmic Brainiac. (Can you be a threat if you're insignificant?) He allegedly will serve a "larger purpose," but, again, we don't learn what that purpose is. (Notice a theme? Also, can you serve a larger purpose if you're insignificant?) Cosmic Brainiac then shows us a collection of moments in time that he's made, specifically of Superman's deaths from doomed timelines. (Superman is also somehow floating in space and watching these deaths during this conversation.) Cosmic Brainiac notes that "our" Superman wasn't the only one to face the Doomsday monster; we again seem to be referring to the events of "Superman: Doomed" here, but I'm not sure. At any rate, Superman accuses Cosmic Brainiac of killing this other Superman that faced Doomsday (again, seemingly from the "Superman: Doomed" story and not the initial "Death of Superman" story). Then, we're suddenly back at the machine, and Cosmic Brainiac denied that he killed this Superman, though this Superman's death informed him infecting "our" Superman with the Doomsday virus. But, again, we get no further information. Superman tries to escape, and Cosmic Brainiac says that he's already tried to escape that 32 times.
Cosmic Brainiac then announces that he has what he wants from Superman: information about his city. Superman says that he won't let him destroy Metropolis, but Cosmic Brainiac says that he's not talking about destroying Metropolis; in fact, he's not even talking about Metropolis. Suddenly, we've returned to the machine, and Cosmic Brainiac has gone quiet. Superman finally breaks the machine, and then busts his way from the room where he's been imprisoned. He finds himself in a barren wasteland, and he stumbles upon another (less cosmic) Brainiac. This Brainiac confirms that Cosmic Brainiac has left and expresses shock that Superman has escaped; he says that his Master was right to be worried about him, because it's always him. (We don't know what Superman "always" does, but presumably we will at some point.) This Brainiac turns into several different versions of Brainiac as he tells Superman that he has several versions of Metropolis, but can't return him to Earth (but, again, we're not given any reason why he can't). This Brainiac (in all his different forms) announces that he's the Keeper of the cities and suggests that Superman pick a Metropolis that makes him happy.
Eventually, the Keeper tells Superman that Cosmic Brainiac was always impressed with Kal-El's father, because he helped him escape death. (Cosmic Brainiac earlier had announced that he was impressed by people that escaped death. Aren't we all?) Then, the Keeper becomes enraged because Cosmic Brainiac has not returned after going to Earth to fetch its timeline. (I know. I'm just going to keep writing here.) He accuses Superman of doing something to him, saying (again) that the Master was right to see him as a threat. But, then, suddenly, he starts exposition-ing. We learn that the Keeper is actually the embodiment of a planet that Brainiac moved outside space and time so that he could place cities on it that he plucked from doomed timelines to judge them. (Um, OK.) We learn that the trapped cities can't escape until they've proved that they're worthy. Superman is outraged, though the Keeper notes that Cosmic Brainiac actually saved them for certain destruction.
Then, just as suddenly, the Keeper expels Superman; since Cosmic Brainiac never returned with a city from Earth, it means that Superman doesn't belong there. (He also conveniently won't remember this experience.) In the absence of the Master, the Keeper decides to undo his "mistake" and set in motion judgement, allowing the strongest city to survive.
In other words, we have Cosmic Brainiac collecting cities from doomed timelines to judge them, though we never learn how he selects the cities, how he judges them, or why he would want to judge them. Presumably, since it's Brainiac, he would be trying to learn something in the process, but we're not told what lesson that he'd be trying to learn. Moreover, for reasons that will hopefully become clear soon, he never returns from his excursion to Earth, forcing the Keeper to take matters into his own hands by setting in motion judgement. (Again, we're never told why Cosmic Brainiac never actually set that process into motion in the first place.) Also, Superman is there because Cosmic Brainiac sees him as a threat, but we don't know why he's one. It's implied that we're in some sort of timeloop (we are outside of time), so Cosmic Brainiac might have observed him defeating him several time. But, again, I'm just guessing here. Also, it's not clear why the Keeper had to act the minute that Cosmic Brainiac was gone for an extended period of time. Did he just go sort of crazy?
In other words? For a zero issue, this issue fails to do its job of introducing the concept in the way that a new reader could understand. I pretty much stick to the Batman part of the DC Universe, and it's clear that I need to be really steeped in the Superman corner of it to understand this issue. If I hadn't already bought the first few issues, I probably wouldn't be continuing with this event.
* (one of five stars)