The Justice League of America battle a giant ice creature. With the defeat of the ice creature, the Justice League of America wonder who summoned them, as no member did. In close proximity to the Fortress of Solitude, Superman leads the Justice league of America there, to imprison the ice creature. Superman leads the Justice League of America into the computer room, to try to determine what the ice creature is. Unseen by all, the ice creature reveals itself to be Doctor Light. After easily escaping the "creature's" cage, Doctor Light steals Superman's sole sample of Amnesium.
Doctor Light focuses a modified weapon on the Amnesium, and steals the knowledge of their secret identities from the Atom, the Batman, the Flash, the Green Arrow, and the Green Lantern. Doctor Light taps the Amnesium to absorb that knowledge for himself. Aquaman notices a strange effect wash over the Justice League of America, but the team members deny any issues. As they prepare to depart the Fortress of Solitude, the afflicted members suddenly become aware that they don't know who they are. Focusing his weapon on the Amnesium, then through a prism, Doctor Light restores the knowledge of their secret identities, but to the wrong heroes.
Certain that something is awry, Aquaman, and Superman, decide to surreptitiously follow the Justice League of America. As Aquaman swims out to sea, he encounters a giant lantern fish, lighting the way. Doctor Light watches, from a monitor in the Fortress of Solitude. Too squeemish to witness what comes next, Doctor Light turns away from the monitor. When Aquaman touches the lantern fish, it explodes, seemingly killing him. Oliver Queen, believing himself to be physicist, Ray Palmer, trips a booby trap, in Palmer's laboratory. Beams of light batter Queen's body. Were he truly Palmer, he could escape, using Palmer's powers, as the Atom. Queen, though, as the Green Arrow, is in dire jeopardy.
Bruce Wayne, believing himself to be Queen, trips a booby trap, in Queen's tenement building. Queen's neighbors become enraged with hatred, and savagely attack Wayne. Hal Jordan, believing himself to be police scientist, Barry Allen, meets with Professor Ira West. Upon seeing Jordan, a stranger, West calls for the police, tripping another booby trap. Jordan is caught inside West's newest invention, a portable jail cell. The golden walls of the cell close in on Jordan. Were Jordan truly Allen, he could easily escape the trap, using Allen's powers, as the Flash. Jordan, though, as the Green Lantern, is in dire jeopardy.
Palmer, believing himself to be Jordan, meets with Arthur Curry, to show him the latest line of Merlin Toys. Unveiling a block of modeling clay, Palmer trips another booby trap. The clay begins to rapidly expand, threatening to engulf and suffocate Palmer. Were Palmer truly Jordan, he could easily escape the trap, using Jordan's power ring, as the Green Lantern. Palmer, though, as the Atom, is in dire jeopardy. Doctor Light has simultaneously set all of these death traps, by dispatching solid light holograms of himself to each of the heroes' respective cities. Suddenly, the monitors in the Fortress of Solitude go dark.
Superman confronts Doctor Light, only to be imprisoned in light rings of kryptonite radiation. The Justice League of America confronts Doctor Light. Aquaman reveals that he reached out to the lantern fish telepathically, first, setting off the detonation. Aquaman then checked with the computers in the Fortress of Solitude, to discover Doctor Light's scheme. Aquaman, as Curry, aided Palmer in escaping from Doctor Light's deathtrap. Palmer, as the Atom, joined Superman, in Gotham City, to convince Allen that he was not Wayne. Curry freed the Green Arrow from Doctor Light's deathtrap. Allen, as the Flash, rescued the Green Lantern from Doctor Light's deathtrap.
Superman rescued Wayne from a horrendous beating. Doctor Light creates two solid light holograms of himself, then flees, releasing creatures from Superman's zoo, as he goes. Doctor Light also creates two solid light holograms of the creatures. Knowing that contact with the holograms will result in a powerful explosion, the heroes use indirect methods to subdue the creatures. The Atom, and the Green Arrow, track Doctor Light to the chamber holding the bottle city of Kandor. Doctor Light creates solid light holograms of the bottle city, and begins hurling them at the two heroes. As Doctor Light lifts the next bottle city to throw, the Atom sees that it casts a shadow, identifying it as the real bottle city of Kandor.
The Green Arrow fires a shaft, with the Atom riding it, at Doctor Light. Realizing that this Doctor Light is a hologram, the Atom causes the arrow to miss, while he snatches away the bottle city of Kandor. Still not realizing that Doctor Light is a hologram, the Green Arrow fires again, setting off a powerful explosion. Aquaman attempts to free Superman, to no avail. Aquaman takes Superman's indestructible cape. Doctor Light creates solid light holograms out of the Flash's super-speed afterimages. Should the Flash stop, the afterimages will collide with him, resulting in a massive explosion. Doctor Light focuses his hate inducing ray on the Batman, who immediately tries to murder the Green Lantern.
Aquaman wraps Superman's invulnerable cape around Doctor Light. The hologram of Doctor Light harmlessly explodes, inside the cape. The Green Lantern knocks the Batman unconscious. Aquaman pulls Superman's cape across the entryway between two chambers. The Flash vibrates his molecules into intangibility, to pass through the cape. His afterimages collide with the cape, and explode. The Green Lantern disarms Doctor Light, while the Atom beats Doctor Light into unconsciousness. Once Superman is freed, the Man of Steel destroys the amnesium. Realizing the Doctor Light's scheme would have failed, had the Justice League of America known each other's secret identities, the Justice League of America unanimously decide to make that information known to any team member.