While putting in a vote to determine which hero to induct into the Justice League, each member is shocked to find that they have all voted for the Atom, a hero of whom they have no memory. Using his power ring, Green Lantern is able to inform the group that the Atom is a hero located in Ivy City who has size changing powers. The group decides to send Martian Manhunter to Ivy City where he can learn more about the hero they all apparently voted for.
While giving testimony in a court case, the Atom himself finds himself suddenly struck with amnesia along with everyone in the room by Mr. Memory. While the judge, jury, and everyone else tries to grab the Atom, he manages to make his escape out an open window. Meanwhile, the Justice League arrives in their various cities of operation, and are attacked by a group of foes who erase their memories and take them hostage. Green Lantern is defeated by Hector Hammond, the Flash by the Pied Piper, Aquaman by Sea-Thief, Wonder Woman by Angle Man, Green Arrow by Dr. Davis, and Martian Manhunter by a strange robed figure just as he finds Atom, who shrinks to microscopic size to avoid being grabbed by the Manhunter.
With his memory restored due to the sudden size shrink, the Atom goes to the heroes’ rescue, and manages to free them from an atomic bowling-ball trap and use Green Lantern’s power ring to restore their memory. Defeating all the criminals, they unmask the robed figure and learn that it’s Batman who has also become victim to the amnesia ray. Tracking down Mr. Memory to his control room, they learn that he’s really their foe, Amos Fortune, who has been using an amnesia device to get revenge on the League. With Amos and the other criminals turned over to the police, the Justice League induct the Atom into their membership, providing him with a special floating miniature chair and miniature emergency signaling device.