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 whom they have no memory of. 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 go to Ivy City and 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 Ivy City, 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. This last abduction was done in front of the Atom who shrank 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 unmasked the robbed 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.

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