Check out a summary of Book One, Book Two and Book Three.Lookout below for spoilers.

Black Adam is finally taken down by the Justice Society and the rest of the heroes from America all upon China’s soil. This is pretty much just an extended battle scene from the pages of 52 #50. We do gain a bit more insight as to how Black Adam was distracted long enough to be changed in to his original form by Captain Marvel in a surprise attack. The Martian Manhunter entered Black Adam’s mind once more and flooded it with the horrors of the destruction of Mars and of all the victims whose lives were claimed by Adam.
In the end, Martian Manhunter claims that in the “moment of searing heat and pain” that severed his psychic link to Black Adam, he both “died and was reborn”. He will no longer deny what he is… J’onn J’onzz. The Manhunter from Mars.

Meanwhile above Earth on the Monitor Satellite, we Monitors discussing the fate of the planet and of it’s heroes. They make the ominous claim that “They must evolve or they will not be prepared. Their darkest hour has not yet arrived.” Presumably this is what Countdown 52 will be leading up to.