While out on separate cases, each member of the Justice League find that their various super-powers fail them during critical moments of their solo adventures. Finding the whole experience fishy after battling the Mirror Master, the Flash in his guise of Barry Allen hears of crimes being committed by a super-powered criminal that mimics their powers. Calling the Justice League together, the Flash tells the others of these fantastic robberies which were used by one crook who could imitate their various super powers.
When they realize that the being that committed the super-crimes was stealing animals with amazingly long life spans, they theorize that the thief in question is attempting to make an immortality elixir. Tracking down other animals that live extended lives, Wonder Woman, Flash, Green Lantern, Aquaman, Batman, Superman and Martian Manhunter decide to go and track down the villain. Wonder Woman is the first to meet the enemy, a robot named Amazo who has duplicated all their powers.
In each instance, Amazo defeats each member of the Justice League and takes them hostage and takes them before his master Professor Ivo. Ivo has them exposed to chlorine gas to knock them out, so that Amazo can use his mimicked Green Lantern powers to erase their memories of them. However, Green Lantern inhales the gas (it being yellow in composition) and exhales it while Amazo is using his imitation power ring powers. Having not been affected by the power, Green Lantern is able to use his power ring to immobilise both Amazo and his master and free his friends.
After explaining how he overcame Amazo’s imitation Green Lantern powers, the JLA turn Ivo to the authorities where he is sentenced to 500 years in prison, after the court case the JLA put the now deactivated Amazo into their trophy room as a monument.