Kara is moved by the story of a missing woman named Izzy and decides to investigate despite Snapper Carr’s order to leave it alone. Kara takes Mon-El with her to the last place Izzy was seen and the duo find themselves thrust through a portal to another planet, Slaver's Moon, where the downtrodden are sold as slaves. The leader of the trafficking ring is none other than Roulette. To make matters worse, Slaver’s Moon has a red sun, which means Kara and Mon-El are stripped of their powers and stuck on the planet with no way home. Meanwhile, back on Earth, Alex blames herself for Kara’s disappearance, fearing she's become too focused on her new relationship with Maggie and too complacent in watching out for her sister.
- The episode's title is a reference to the unproduced Superman movie Superman Lives. The episode's director, Kevin Smith, wrote the original screenplay for the film.
- Winn says "You just hit a button and you're thinking with portals", a phrase that was first introduced in 2006 with the teaser trailer for the video game Portal which ends with the line "now you're thinking with portals.".
- An Earth Thirty-Eight Dominator can be seen when Supergirl, Mon-El, and the rest of the humans are captured. Kara mentions that she hates the Dominators, indirectly referencing the four-night crossover event, , in which she went to Earth One and fought the Dominators of that universe.
- When Winn is left alone at the portal, he says a few times, "I am not a red shirt". In the Star Trek franchise, a "redshirt" is a term used by fans to denote a character wearing a red Starfleet uniform that is killed, typically expendable characters with little significance to the plot besides their death.
- When Kara asks Winn why he is wearing sunglasses, he answers "The future is so very bright". This might be a reference to the Timbuk3 song "The Future's So Bright, I Gotta Wear Shades".
- Kara wants to watch the TV series The Night Of with Alex.
- Winn compares the transmatter portal to a Stargate, a reference to the 1994 movie of the same name.
- When Alex (Chyler Leigh) explains to Maggie (Floriana Lima) that she doesn't want to go to work and that she just wants to stay home with her instead, she fake coughs and says, as an excuse, "I've got the black lung!". This line wasn't scripted; it was added later when on set, Chyler said it as a joke when talking with the cast and crew and they all laughed and loved it. Thinking it would be a good line for the scene, they added it in.
- The line Mon-El says, "Start the car!", was also improvised on set and kept in by the episode's director.
- At the end of the episode, while escaping Slavers' Moon, Winn exits through the portal twice. He can be seen being pushed through the portal by Supergirl at the 32:08 mark, and then standing next to her still on Slavers' Moon at the 32:24 mark and going through it a few seconds later.
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