Flash fears he has completely destroyed his home town.
At an observatory on Mt. Vista, near Central City, astronomers discover that two massive pulsars have converged, and are on a collision course with Earth. Iris Allen arrives to interview the the scientists just in time for them to discover that Central City is at ground zero for the impact. As the scientists panic, Iris rushes outside to contact Barry Allen, hoping that the Flash can save the city.
Barry rushes away from work, and as the Flash, creates an ionic updraft that seems to shield Central City from the impact, diverting the combined pulsars back into space. However, the exertion causes him to pass out. When he comes to, he finds a giant crater where Central City used to be. It appears that Flash has destroyed his city in attempting to save it.
While mourning the loss of Iris and the other residents of Central City, Flash "hears" a distress call coming from the crater, though it seems to exist only in his mind. He follows the signal and discovers what looks like a slightly larger-than-human mud creature. The creature attacks, and as Flash thinks about his strategy, he discovers that it is also reading his mind. By spinning into the ground at super-speed, Flash creates a quicksand pit to trap the creature. At that point, he discovers that the creature is actually just a mud-covered (but abnormally tall) human woman wearing a space suit.
The woman tells Flash her story. Her name is Zoral, and she comes from the year 4005. After some discussion, Flash and Zoral decide that Flash's super-speed rescue of Central City must have caused her and the city to switch times and places. Just then, Zoral's vibrational frequency starts to return to normal, which will cause her to return to her own time. Flash grabs her just in time, and is transported to 4005 along with her.
As the pair travels through time, Zoral explains to Flash that in her time, people's emotions are controlled by "anti-violence emitters" that prevent them from killing or even feeling strong emotions. Further, Zoral's boss Dr. Yom is working on a device called the quantum-time-shift-resolver, which will allow him to bring entire cities from the past into the future to serve as living museum exhibits. She suspects that he will take the appearance of Central City as proof that the device works.
When Flash and Zoral finally arrive in the future, they are immediately attacked by a patrol armed with anti-violence ray guns. As Flash struggles against one of the patrolmen, Zoral attempts to use her own pacifying gun to help Flash, but accidentally shoots him instead. The two of them are then taken prisoner, and brought before Dr. Yom. As they are being led in, Flash catches sight of Iris on a view screen broadcasting video from Central City, and the surge of emotion he feels overrides the effects of Zoral's anti-violence gun. He continues to act as if he has been pacified, though.
Just as Zoral suspected, Dr. Yom believes it was his device that brought Central City to 4005, and not the ionic vacuum Flash created. Zoral and Flash explain what really happened, and eventually Yom accepts their explanation. However, he reveals that scientists in 4005 are the only people not subjected to the anti-violence emitters. He is aware of Flash and the Cosmic Treadmill, and attempts to kill Flash so he can take the treadmill and integrate it into the quantum-time-shift-resolver.
Flash avoids Yom's attacks by slowing his molecular vibrations so that he slips backward in time to five minutes earlier, where he grabs Zoral's anti-violence gun and shoots Dr. Yom with it. Under the gun's effects, Yom realizes the immorality of his plans, and allows Flash to send Central City back to 1968. Flash and Zoral say their goodbyes, and Flash returns to his own time, where he and Iris are reunited.