A group of heroes and villains, including the likes of the Golden Age Superman of Earth-2, have been assembled by the enigmatic being known as the Monitor and his partner, Harbinger to defend monolithic machines that may halt the advance of the destructive anti-matter wave.
The story starts at the end of time when a tribesmen known as Anthro who stops a massive stampede of mammoths he calls "serpent noses". He is successful but notices a huge futuristic city on the horizon, he turns to his tribe to show them the city but when he does the city is gone along with the mammoths. The Mammoths end up in the thirtieth century were the Legion of Superheroes try to stop them from running amok.
In Gotham, Batman stops the Joker but in the middle of everything a decaying Flash shows up and pleads with Batman to save the world which he says is dying. The Flash decays into nothingness while the Joker runs away.
Back at the Monitor's satellite his chosen heroes and villains are gathered to help him stop the end of all existence. Everyone is confused and argues but decides in the end to help the Monitor. It is then that the Harbinger sends them all over and to different times.
On Oa the Guardians of the Universe discover that the universe is ending and they try to figure out how to prevent their universes destruction. It is at this time when the main battery speaks to them and tells them that everything ends with them. While in Metropolis Superman meets with Batman who explains what happened with the Flash. As they are talking Pariah shows up and tells them their world is going to be destroyed. He then disappears.
In the time of between the twentieth and thirtieth centuries Kamandi climbs one of the Monitors towers. As he wonders were it came from a shadow pops out of the tower and cuts his rope sending him to his death. He is however saved by an aging Superman. Superman, Solovar and Dawnstar were sent to guard the Monitor's tower but they are not there long when they are attacked by shadows. Kamandi is the first to be attacked but he is saved by Solovar.