Forgot to paste in the first bit of my summary. This is all of it.
Darkseid upon winning the war in heaven falls broken to Earth dragging reality with him. His opening moves disable the trinity and remove Earth's lanterns leaving earth defenceless. Darkseid easily conquers the planet. The worlds only hope is the newly reborn Barry Allen.
Meanwhile Superman has travelled into 4th dimensional space along with other trans-dimensional Supermen to find a way to save Lois. On the monitor world he and Ultraman must combine their energies to a colossal thought robot to Fight Mandrakk, formally Dax Novu the original Monitor from crisis on infinite Earths. Mandrakk is killed after a battle that shakes reality, but his essence infects one of his minions and Mandrakk is reborn.
On Earth, the resistance is faltering. Batman looses is life as he mortally wounds Darkseids body. Superman returns breaking Darkseid's forces, just as the Flash's arrive leading Death to Darkseid. the combined efforts of the heroes and villains break Darkseids hold on the Earth, but are too late to save reality.
On a strange amalgam of the various Superhero bases floating in the shattered remains of reality, Superman and the worlds greatest scientists work together to build the ultimate expression of technology, however as they work other realities are falling victim to Darkseid. Superman and Darkseid have their final battle, but the effort weakens Superman.
Mandrakk returns, but Superman is able to activate the Miracle machine and makes his wish. Mandrakk is set upon by the Supermen of the multiverse, the angels of the Pax Dei, The new forever people, Captain Carrot and the Zoo crew and the Green Lantern corps. The heroes rebuild existence and things return to normal. The monitor world returns to the primal expanse that formed it leaving the stories of the DCU to grow unfettered.