Hal Jordan is on vacation in Paris, France, riding the subway when another train approaches, threatening a collision. He quickly changes into Green Lantern to help, but before he can do anything, Sinestro appears and saves the day. Later in Gotham City, Batman and Robin try to stop a couple of bank robbers, but Toyman intervenes and prevents their escape, enabling the police to arrest them. Some time later in Metropolis, Wonder Woman and Hawkman come to the aid of a passenger blimp in distress. Wonder Woman nearly falls to her doom when she gets blasted in an effort to seal the leak, but she's saved by Grodd while Bizarro gets the blimp to safety. The villains announce they and the rest of the Legion of Doom have decided to become the Legion of Good, to everybody's surprise. The SuperFriends, hearing more of the Legion's various selfless deeds at the Hall of Justice, receive a distress call from the planet Santar, which is in danger as solar flares from its twin suns ravage the planet. However, the Legion pick up the communiqué as well, claiming they're already on their way to help. But Luthor's intentions are false as instead he decides to take the Legion of Doom into the future where the SuperFriends won't be in the way to stop them. Only the Riddler stays behind in the present to leave clues on Santar to put the SuperFriends on a wild goose chase.
The Legion travels to the year 3984 where they help the Barlocks, a subhuman race that resides primarily in dark caves, conquer Earth's capital city of that time. Back in the present, the SuperFriends receive a second distress call from planet Santar, revealing they've endured worldwide devastation since they've received no aid. With the SuperFriends deceived, Wonder Woman, Black Vulcan, and Hawkman race there to see if there's any last chance to help, but it's too late. Riddler appears as an image on what seems to be the Hall of Doom to leave a riddle, but when the three SuperFriends give chase, it explodes. Black Vulcan demonstrates it was an inflated replica. But more trouble occurs since the replica was filled with a gas that's in danger of breaking down their molecular structures. Black Vulcan is able to use his powers to create a magnetic field to make the heroes solid again. The group contacts the Hall of Justice to replay Riddler's riddle. Batman and Robin decipher it and conclude they need to go to the Pyramids of Egypt. Samurai accompanies them and search the pyramids where they find Riddler at the last one, but he seals them in a tomb. Batman is able to get them out, but Riddler leaves another clue behind. The group figures the Legion is 10,000 years in the future and relays the info to Superman, Flash, and Green Lantern, who use their abilities to travel forward in time. They find no human life, but they're captured by giant, mutant spider creatures that are resistant to their powers. In 3984, the Legion of Doom having successfully conquered Earth's capital city and decide to expand their conquests to several galaxies, attacking their main home worlds and reveling in their increasing power. Further in the future, Superman, Flash, and Green Lantern are able to combine their powers to escape from the mutant spiders and come across an old library which has a history book detailing exactly when the Legion of Doom made their conquests. The three travel back to 3984 where they find the Legion and engage them in battle. Superman and Green Lantern are able to stop their attack ships, while Flash is able to subdue the Barlocks. Power is returned to the true rulers of Earth and the other conquered galaxy planets as the three heroes return the Legion of Doom to the present. With the villains caged at the Hall of Justice, Riddler wonders how the SuperFriends were able to pinpoint exactly when in the future they were and Superman shows them the history book. They were also confident the Legion's rule would be very brief as the book also indicated they would be captured shortly afterward by the SuperFriends.