Police Forensics Scientist, Barry Allen, is called down to witness a line-up. All four men in the line-up are Allen's friend, test pilot Hal Jordan. Using his power ring, Jordan telepathically communicates with Allen. Spying the telltale glow of Jordan's power ring, Allen gets the real Jordan remanded into his custody. After test flying the experimental X-35, in low Earth orbit, over Central City, Jordan decided to call on Allen. Outside of police headquarters Jordan encountered a man who looked just like him. This man attacked Jordan, and was swiftly joined by two more exact twins of Jordan. The police broke up the fight, which led to Jordan's appearance in the line-up. Allen and Jordan decide to investigate the situation, as the Flash and Green Lantern.
The two heroes journey to Coast City, so the Green Lantern can renew the 24 hour charge on his power ring. Suddenly the three Jordans walk in on them, garbed as Green Lanterns. One of the Green Lanterns explains the situation. While Jordan was test flying the X-35, a light beam that Jordan took for the "Glenn Effect", was really a duplication ray, fired at him by T.O. Morrow. Inspired by his name "Tomorrow", Morrow set about to invent a time machine. Though he failed in that endeavor, Morrow was able to invent a device that allowed him to view the future. Morrow then studied future inventors, and recreated their future technology in the present. One such future machine was the duplicator.
Having created three exact duplicates of Jordan, Morrow learned that Jordan was the Green Lantern. Bored with using his future technology to simply rob banks, Morrow decides to have his Green Lanterns challenge the real Green Lantern, as well as the Flash. The Green Lanterns head off to Paris, London, and New York, to steal the Mona Lisa, the Statue of Liberty, and a collection of fine gold coins. The Flash races across the Atlantic Ocean, to Paris, to stop the first theft. There he sees Morrow's Green Lantern lifting an entire wing of the Louvre, high into the air, with his power ring. The Flash races to a nearby circus, where he allows himself to be fired at the Louvre, from a cannon. Morrow's Green Lantern uses his power ring to animate the statues into attacking the Flash, while also endowing them with super-speed.
When that attack fails, Morrow's Green Lantern uses his power ring to collapse the very structure of the Louvre around the Flash. The Flash repels and deflects the debris back at his foe, who shields himself with a ring constructed force field. Painting himself yellow, the Flash charges Morrow's Green Lantern. Morrow, though, has removed the weakness to yellow from his Green Lanterns' power rings. Spinning at super-human speed, the Flash sloughs off the paint, creating a barrage that blinds Morrow's Green Lantern long enough for the Flash to deliver the knockout blow. Using the power ring, the Flash cages Morrow's Green Lantern, then heads to London. In New York, Green Lantern engages his evil twin.
Morrow's Green Lantern fires off spheres of yellow energy, that will explode on contact. Green Lantern dives for the Hudson River, parting the waters with the power of his ring. With the energy spheres in pursuit, Green Lantern swiftly surfaces, while releasing the river's walls of water. The energy spheres explode harmlessly beneath the river's surface. Green Lantern rams the base of the Statue of Liberty, driving it upwards, into his twin, knocking Morrow's Green Lantern out. After caging his opponent with his power ring, Green Lantern heads to London. Encountering the Flash en route, Green Lantern uses his power ring to create a more stable platform for the Flash to run on. The two heroes encounter Morrow's Green Lantern, as he flees across the rooftops of London.
Morrow's Green Lantern fires a power ring generated projectile at the Flash, then swats the Green Lantern out of the sky. The Green Lantern lands in the river Thames, which Morrow's Green Lantern transforms into quicksand. Vibrating at super-speed, the Flash allows the projectile to harmlessly pass through him. The Green Lantern uses his power ring to lift the Flash into the sky, to confront Morrow's Green lantern. As soon as the Flash is held in the power ring constructed hand, though, the Green Lantern stands up in the quicksand, revealing that he is actually one of Morrow's Green Lanterns. Suddenly, a power ring constructed rope appears to pull the Flash away from Morrow's Green Lanterns. It is the real Green Lantern.
In New York, Morrow's Green Lantern used his power ring to enslave Green Lantern's mind, then forced him to cage himself. Then he stole Green Lantern's power ring, so that he could not escape. Morrow's Green Lantern then rendezvoused with the Flash. However, creating the power-ring runway for Flash to race along gave him away. Only one of Morrow's Green Lantern's yellow-resistant ring constructs would have remained stable, while in contact with the Flash's yellow boots. The Flash willed the ring he took off of Morrow's Green Lantern, in Paris, to seek out the real Green Lantern, in New York. Green Lantern used the power-ring to free himself, then journey to London, and the Flash's rescue. Suddenly, Morrow's Green Lanterns dissipate into thin air.
Green Lantern uses his power ring to command the Morrow power ring to lead them to Morrow. The two heroes storm Morrow's laboratory complex, only to run headlong into a trap. The Green Lantern throws a shield around himself, and the Flash, to protect them from Morrow's laser gauntlet. Spying Morrow's duplicator, the Flash realizes that Morrow, himself, is a duplicate. The Flash throws the lever to erase the Morrow duplicate. The lever, though, has been booby-trapped. The Flash and the Green Lantern are caught in the center of an explosion. With the two heroes seemingly slain, the real Morrow comes out of hiding. Suddenly, the two heroes reveal that their "deaths" were merely a ruse. in his haste to flee, Morrow trips over a cable, falls into a pit, and is electrocuted.
Back in Central City, the Flash and the Green Lantern, as Allen and Jordan, are joined for dinner by their respective girlfriends, Picture News Reporter, Iris West, and Carol Ferris. To surprise Jordan, Ferris's hairstyle and attire exactly mirror West's, causing both Allen and Jordan to think, momentarily, that West has a twin.