During a training session, Supergirl, Green Lantern, and Green Arrow are pulled into the 30th Century by Brainiac 5. The Legion of Superheroes are facing a crisis, and the Leaguers were abducted because of historical records stated they journeyed to the future. However, Brainiac 5 doesn't tell them that the records also state only two went back...
- Badass in Distress: The entire Legion of Superheroes save Bouncing Boy (for a while anyways) and Brainiac 5 has been caught and brainwashed by the Fatal Five.
- Call-Back: Bouncing Boy is about to say that John is the father of a certain famous figure before he tells him to stop talking before he creates a time paradox. John had met his son with Shayera, Warhawk, back in "The Once and Future Thing" during another time-travelling escapade, which made his Love Triangle between Shayera and Mari more complicated. John doesn't know if the future where he has Rex with Shayera has changed, and to preserve the space-time continuum and keep himself from having to think any harder about it, it's better that he doesn't know.
- Call-Forward: The Z-8 robots appear during Supergirl's training simulation and now possess the holographic technology that Zeta used so often.
- Curb-Stomp Battle: The five heroes get ambushed by Emerald Empress and Persuader. They all get captured, except for Brainy, who manages to free Kara and accidentally frees Ollie.
- Danger Room Cold Open
- Exact Words: History says that Supergirl never returned from the future. Brainiac 5 and Bouncing Boy assume that it means she died, but no one except her considers that it was because she chose to stay.
- Fish out of Water: Ollie tells Clark that Kara must feel like this. He also shoots down Superman when he tries to say he can emphasis, as Clark arrived on Earth as a baby and was Raised by Natives and naturally grew into his powers, while Kara spent most of her life on another world was much more advanced technology, and just suddenly had her powers all at once.
- I Choose to Stay: Kara decides to stay in the 30th Century with Brainiac 5 at the end.
- Mundane Utility: Kara mentions that back on Argo, TV remotes were equipped with psionic functions so that if they ever got misplaced, the user could just think at it and it would set off a beeping sound so it could be found.
- My Sensors Indicate You Want to Tap That: Downplayed. Brainiac 5, who is both a biological living being and a machine, runs a system diagnostic on himself when Ollie asks if he feels different around Kara and finds that his body does act differently, such as shortness of breath. Apparently, he thought it was because of guilt.
- Mythology Gag:
- John cradles the seemingly dead Supergirl in an echo of the cover for Crisis on Infinite Earths #7.
- Emerald Empress mentions that Green Lanterns are rare around Earth. In the pre-Zero Hour comics, Universo, a Legion of Superheroes villain, used to be a Green Lantern until he tried to use it to see the Dawn of Time in order to become a god. As a result, the Guardians of Oa confiscated his ring and banned the Green Lantern Corps from Earth.
- Oh, Crap!: Brainiac 5 has one when he realizes that Supergirl is confusing him for his malevolent predecessor.
- And at the end, this is John and Ollie's reaction when Superman asks who, exactly, is this boy his cousin's met.
- Stable Time Loop: The records say that one hero of the three brought to the future never came back... because she chose to stay.
- Wham Line:Supergirl: History says Supergirl never came back from the 31st century... because she decided to stay.
- What Is This Thing You Call "Love"?: Played with. Brainiac 5 knows what love is, but he's denial about his attraction to Kara. When Ollie prods him about it, Brainiac starts to realize from the way he's acting that he really is into Kara.