While the team went through a training exercise, Batman learned that the man they thought to be Trident was actually Karate Kid from the Legion of Superheroes - a team that existed in the 31st Century. They questioned him and he told them there were seven of them somewhere in this time period. The JLA and JSA got together - Starman was another of the seven.

Batman, GeoForce, Starman, and Sandman went to Arkham Asylum. Dr. Destiny had broken free and was holding Dream Girl, another of the seven. She was freed.
Cyclone, Red Tornado, Stargirl, and Superman headed to the Fortress of Solitude - a Legion flight ring was detected there. He had a trophy room with statues of all the Legion members he'd worked with. One of them turned out to be the real Wildfire.

Mr. Terrific examined a belt that had come with Wildfire, but could find nothing special about it.
Vixen, Flash (Jay), Wildcat, and Green Lantern (Hal) visited Gorilla City and found another of the Legion: Timberwolf. While they were there, an albino gorilla was born.
Powergirl, Red Arrow, Hawkman, and Hawkgirl found another on Thanagar: Dawnstar. PG warned Roy about Hawkgirl - she'd tried to have a relationship with Hawkman.
The Legion all had what they called Lightning Rods - when lightning struck, one of them would die and someone else would return from the dead.

After realizing the Legion was gone, Superman explained to the JLA and JSA what the Lightning Rods were used for - he'd been a part of a previous use with them.
The Legion split up and prepared for lightning.
Damage, Hourman, Liberty Belle, Black Lightning, and Wonder Woman found the final Legion member: Triplicate Girl. They were attacked by a sentient computer / robot. The rest of the JLA / JSA team arrived to lend a hand and let them know their Legion members had escaped.
Superman soon realized they were fighting a construct created by Sensor Girl - the real seventh member.

Lightning struck - Wally West and his family (wife and two kids) appeared. The Legion returned to their time, but Karate Kid and Starman stayed behind.
Wally joined the Justice League.

Red Arrow and Vixen were trapped in a toppled building under water. Vixen confided in him that her powers changed when they fought Amazo - she could no longer gain the powers of animals, but the powers of other metahumans.
They escaped when they found out which way was up.

Aquaman and Martian Manhunter watched the League as they took monitor duty. Roy introduced his daughter to Kendra. Dinah warned Kendra not to hurt her "boy," but they later slept together.
Superman, Wonder Woman, and Batman watched as GeoForce met with Deathstroke. Brion revealed to Batman that he'd been approached by the villain.