- For the eponymous character, see Nora West-Allen.
- For other uses of the name "Nora", see Nora (disambiguation).
- "My name is Nora West-Allen, and I'm the fastest woman alive. When I was a child, my father disappeared in something impossible. Then I grew up and became the impossible. Now I'm trying to live up to the legacy he created so that one day, I'll stop him from ever disappearing. I'm XS. How schway is that?"
- —Nora West-Allen
After an unexpected guest from the future, Nora West-Allen, appears at their home, Barry and Iris must figure out how to get her back to the future without disrupting the timeline, even more than she already has. Team Flash must work together to send Nora back, while simultaneously fighting off another villainous meta.
- Daniel Cudmore previously played Jackhammer in the Arrow episode "" in addition to providing the motion capture for Grodd in the DC's Legends of Tomorrow episode "".
- Barry suggests that Nora could "Marty McFly herself out of existence", referring to the protagonist of the 1985 film Back to the Future, who accidentally interferes with his parents' first meeting whilst traveling back in time, nearly erasing himself from existence.
- While describing the existence of the Multiverse, Ralph makes mention of an Earth without "that last Indiana Jones movie", referencing the 2008 film Indiana Jones and the Kingdom of the Crystal Skull, which was panned by audiences.
- Cisco calls Nora "Billy Pilgrim", telling her that she is no longer "unstuck in time", both references to the Kurt Vonnegut novel Slaughterhouse-Five.
- This episode features many references to older episodes:
- Ralph mentions the possibility of Barry creating a timeline where the former died in the particle accelerator explosion. Before Barry created and undid Flashpoint, Ralph did die in the particle accelerator explosion, as mentioned in the first season episode "".
- Barry teaches Nora to phase, closely quoting what "Harrison Wells" had said to him when teaching Barry to phase in "".
- Iris mentioned the time Barry traveled back in time and recruited Leonard Snart for help in "".
- Ralph mentions the possibility of a world where everyone is evil. This occurred through the events of . Earth-2, as seen in "" and hinted in the episode "", also fits this description.
- Iris mentioned the time Barry traveled back to 2015 to get help from Eobard Thawne in "".
- Ralph mentioned how Eddie killed himself in "".
- Wally and Nora mention how Wally fought the ghost of Elvis Presley's brother and how he met the actual Elvis Presley in the episode "".
- Nora mentions the time Barry ran on water to fight King Shark in "".
- The picture Nora was looking at of Team Flash was taken by Barry in "".
- Iris mentions the time Barry tried to save her from getting killed by Savitar, which happened throughout the second half of Season 3.
- Barry states, "Nora shouldn't be here", which is one of the quotes he said after coming out of the Speed Force in "".
- Nora mentions the time Barry used the tachyon prototype and accidentally traveled to Earth-38, where he met Supergirl for the first time in "" (the meeting itself was shown in 's "").
- At one point, Iris tells Barry that "[Nora's] not worried about the science, she's worried about the scientist". This is a subtle reference to Barry first appearing in the shared multiverse in the season 2 episode "".
- Nora's monologues at the beginning and the end of the episode are similar to the monologue given by Barry during the introduction to episodes in the first season.
- Barry's Season 1 monologue:
- "My name is Barry Allen and I am the fastest man alive. When I was a child, I saw my mother killed by something impossible. My father went to prison for her murder. Then an accident made me the impossible. To the outside world, I'm an ordinary forensic scientist. But secretly, I use my speed to fight crime and find others like me. And one day, I'll find who killed my mother and get justice for my father. I am The Flash."
- Nora's monologues:
- At the beginning of the episode:
- "My name is Nora West-Allen and I'm the fastest woman alive. When I'm from, 30 years from now, I'm the guardian of Central City. I'm a speedster; just like my dad. People call me 'XS'. Every day I hope to live up to the legacy of The Flash. But I've still got a long way to go."
- At the end of the episode:
- "My name is Nora West-Allen and I am the fastest woman alive. When I was a child, my father disappeared in something impossible. Then, I grew up and became the impossible. Now I'm trying to live up to the legacy he created, so that one day, I'll stop him from ever disappearing. I'm XS. How schway is that?"
- At the beginning of the episode:
- Barry's Season 1 monologue:
- Nora mentions a future battle involving King Shark and Grodd, foreshadowing the events of "" later in the season.
- This may also be a nod to the Season 3 episode "", when after Grodd was defeated and mentioned to have been locked up at A.R.G.U.S., Caitlin said that he can be thrown into the same cage as King Shark (who's also in A.R.G.U.S. custody) for all she cares, since any good in him is long gone. Cisco then stated that was a fight he'd pay money to see.
- This episode marks the second time in the shared multiverse where a season premiere takes place immediately following the previous season’s finale. The first time was the Season 2 premiere "", which picks up exactly where "" left off.
- This is the twelfth episode in the Arrowverse, and the fourth episode of , to be named after a character in a civilian sense, after "", "", "", "", "", "", "", "", "", "", and "".
- The Flash family phasing the crashing plane through the buildings and into the water is an adaptation of when Barry did the same thing in the third issue of his New 52 comic, with the shot of the plane hitting the water a direct copy from the comic.
- Barry and Nora mention the fictional Happy Harbor, Rhode Island. In the DC comics, this was the location of the Justice League's first headquarters, as well as the main setting of the animated series Young Justice.
- The slang Nora often says in this episode (and numerous times in later episodes throughout the season), "schway", originated from the TV series Batman Beyond, where it is used by many of the teenage characters in the future Gotham City.
- Nora mentions that a man named Ryan Choi made Barry's new suit. In the DC comics, Ryan Choi is a student of Ray Palmer and his successor as the Atom.
- Ralph states that a nonexistent individual, Cameron Mahkent, signed off on Caitlin's father's death certificate. In the comics, Cameron Mahkent is the super-villain Icicle.
- This is also a reference to Caitlin's father's cryokinetic-powered villainous alter-ego, Icicle.
- After Barry puts on the Flash ring, a close-up is seen of the ring on his hand, and it's shown that he's wearing it on his middle finger. When the suit comes out of the ring in the next shot, Barry is wearing it on his ring finger.
- Iris mentions that Barry ran to 2020 to learn Savitar's identity, but Barry ran to 2024 to do this.
- Nora says that the old suit Barry uses in this episode is the one he wore when he ran on water to fight King Shark. However, after Barry fought King Shark, that suit was destroyed when Barry was absorbed into the Speed Force in "" when Team Flash recreated the particle accelerator explosion to restore Barry's powers after they'd been stolen by Zoom. Barry then received a new suit from the Speed Force, which was identical to the one he'd had (and been wearing) when duplicating the particle accelerator explosion. Therefore, the old suit he used here couldn't have been the one he wore when he battled King Shark.
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