The Justice League of America unanimously vote the Atom in, as their newest member. Upon doing so, however, none of the members can actually remember who the Atom is. The Green Lantern uses his power ring to probe his own memories. The power ring reveals the early history of the Atom. J'onn J'onzz, the Manhunter from Mars, offers to go to Ivy Town, to make contact with the Atom, and resolve the mystery. The Atom offers testimony in a criminal case. A mysterious man, hiding in the shadows of the courtroom, erases the Atom's memory. No one else in the courtroom possesses any familiarity with the Atom, either. In a panic, the Atom flees the courthouse. Unbeknownst to the Atom, he is under observation by the Sea Thief, the Pied Piper, Hector Hammond, the Angle Man, Doctor Davis, and Mister Memory.
The demonstration a success, Mister Memory outfits the other super-villains with his "De-Memorizer". The Green Lantern battles against Hector Hammond. Unable to defeat the Green Lantern using his own powers, Hammond resorts to using the de-memorizer. The Green Lantern's memories are erased. Hammond turns the Green Lantern over to Mister Memory. The Flash battles against the Pied Piper. Unable to defeat the Flash using his own powers, the Pied Piper resorts to using the de-memorizer. The Flash's memories are erased. The Pied Piper turns the Flash over to Mister Memory. Aquaman battles against the Sea Thief. Unable to defeat Aquaman using his own powers, the Sea Thief resorts to using the de-memorizer. Aquaman's memories are erased. The Sea Thief turns Aquaman over to Mister Memory.
Wonder Woman battles against the Angle Man. Unable to defeat Wonder Woman with his own powers, the Angle Man resorts to using the de-memorizer. Wonder Woman's memories are erased. The Angle Man turns Wonder Woman over to Mister Memory. The Green Arrow battles against Doctor Davis. Unable to defeat the Green Arrow using his own powers, Doctor Davis resorts to using the de-memorizer. The Green Arrow's memories are erased. Doctor Davis turns the Green Arrow over to Mister Memory. J'onn J'onzz, the Manhunter from Mars locates the Atom. To escape, the Atom shrinks down to microscopic size. Using the de-memorizer, Mister Memory, personally, erases the Martian Manhunter's memories. Still shrinking, down to sub-atomic size, the Atom's memories return.
The Atom grows to six inches in height. The Atom sees Mister Memory leading J'onn J'onzz, the Manhunter from Mars, away. The Atom follows Mister Memory, to his secret lair. The Atom watches, as Mister Memory meets with the other super-villains. After the crooks depart, the Atom attacks Mister Memory. The Atom takes out Mister Memory, with one punch. As Mister Memory falls to the floor, however, he knocks over a lamp, that topples down on the Atom. Mister Memory recovers before the Atom. Mister Memory places the Atom in an explosive gas-filled glass sphere. With the Justice League of America standing like bowling pins, Mister Memory bowls the Atom at them. By increasing his weight, then slamming against the sides of the sphere, the Atom is able to change the sphere's course. Shrinking down, the Atom escapes the sphere.
The Atom topples the Green Lantern. Grabbing the Green Lantern's power ring, the Atom is able to create a power ring constructed hand, that catches the next hurled explosive. Still using the power ring, the Atom immobilizes Mister Memory. Using the power ring, the Atom restores the Justice League of America's memories. MIster Memory is revealed to be the Batman. The Batman's memory has also been erased. Restoring the Batman's memory, the Justice League of America learns that the Batman had been taken, during a conflict with the Joker. The Batman was brainwashed into becoming Mister Memory. J'onn J'onzz, the Manhunter from Mars, tracks the signal, given off by various electronic devices sewn into the Mister Memory costume, to the secret lair of Professor Amos Fortune. After rounding up the other criminals, the Justice League of America convenes, at their headquarters, to officially induct the Atom into their ranks.