Spoiler warning: This article is updated through the Season 4 finale.
Once might have just been a fluke, but this is now
twice three four five times that The Flash has teased a “mystery girl” who seems to know Barry and Team Flash pretty well (while they don’t recognize her). A conspiracy forms! Back in the Supergirl portion of “Crisis on Earth-X,” we first met a waitress (played by Jessica Parker Kennedy) who was not only really excited for a wedding of two people she wasn’t expected to know, but reminded Barry to be sure to say “I do.” Notably, thanks to Felicity’s interruption of Barry and Iris’ second wedding, the Flash duo did not seem to make that particular vow, leading to a theory that this mystery girl is from the future — and possibly Barry and Iris’ daughter.
While that might all have been chalked up to some crossover craziness, the mystery girl made a second appearance in “The Elongated Man Rises,” where she happily picked up a Jitters tab for Ralph and Cisco. Again, she was super smart and awkward and seemed like she knew the two, though they didn’t recognize her. Most tellingly, she then went over and started writing down some symbols in a journal.
If those symbols look familiar, we’ve seen them a few times before on the show. First, when Barry was freed from Speed Force prison and still pretty crazy at the start of Season 4 he was writing those symbols everywhere. (Remember “this house is bitchin’?”) We’ve also seen them appear on The Thinker’s face (before he swapped bodies), which could mean they didn’t originate with the Speed Force, but are in fact a way to defeat DeVoe.
Which brings us back to the question of: who is the girl? As mentioned, the most prevalent theory is that she is Barry and Iris’ daughter or granddaughter who has sped to the past to help free Barry from Iron Heights and clear his name. The one calculation DeVoe may not have been able to make is one of Barry’s progeny coming back to save him … unless that is also part of DeVoe’s masterplan, and the whole Allen family through the ages is being caught up in his web. After all, if she is Barry’s daughter, she likely inherited his desire to tinker with the timeline as often as possible, like going back and changing the past. But you do you, Allens!
In the comics, Barry and Iris have twins named Dawn and Don, who both inherited a fraction of their father’s speedy abilities. While The Flash likes to pay homage to comic characters and plotines, it never feels beholden to interpret them exactly as they are written, so who knows that (1) if this is Dawn (2) her powers are the same as in the comics. She could have full speed abilities, or even some meta power we don’t yet know of.
There’s also a chance that she might not be Barry and Iris’ daughter at all — she could be another member of Team Flash’s daughter, or someone who becomes close to the team somewhere else in time. Either way, it seems like she’s definitely a friend and not a foe, and her knowledge of this symbol language seems like an important connecting pattern running in the background of this season. Who knows when we’ll see her again, but given her second appearance now, it seems like she will be playing a key role in Team Flash’s future.
Update: In “Enter Flashtime,” the episode concluded with Caitlin and Harry grabbing coffee at Jitters, and Caitlin just starting to tell him about how she felt Killer Frost’s concern for her if the bomb really went off. But just as she did, the Mystery Waitress appeared and spilled a Killer Frost coffee (of course) all over their table. After saying she was supposed to be meeting people there for the first time — in a super fast and awkward way that felt more like Arrow‘s Felicity than anyone from The Flash — Caitlin and Harry depart saying they hope it goes well, while our waitress gives a (sinister?) “It did.”
So what does that mean? Could this be another machination of DeVoe? It seems clear that this character is a speedster, so was DeVoe able to harness those powers as well? Another possibility is that Jay Garrick mentioned he was training up a new speedster (a “she”) on Earth-3 — could this Mystery Girl be connected to that? And does it make it more or less likely that this is Barry and Iris’ daughter or granddaughter since she appeared to interrupt Caitlin telling Harry about a further emotional connection with Killer Frost. Saving her or sabotaging her?
Update 2: In “Therefore She Is,” the episode’s stinger revealed a vital new clue about the identity of the Mystery Girl: she is definitely a speedster. And what’s more, she had both purple and yellow lightning when she sped away (before, tellingly, Iris spotted her) — which are Barry and Iris’ speed colors. So it seems pretty obvious that she’s their daughter or granddaughter. This all happened, by the way, when she shows up to Cecile’s baby shower and delivers a gift from “someone who wanted you to know how special you are, someone who understands that time is precious and ‘right now’ is all we’ve got (relatively speaking).” Ominous words! Expect to get a definite answer to who she is by the season finale (which is coming up soon).
Update 3: Confirmed! The Mystery Girl is Barry and Iris’ daughter, Nora. In the Season 4 finale, “We Are the Flash,” Mystery Girl knocks on the door of Joe’s house while everyone is celebrating the birth of Joe and Cecile’s daughter. Once everyone sees her, they call out all of the times they spotted her throughout the season, and she admits that she’s Nora West-Allen, from the future, and that she’s made a “big mistake.” Earlier in the episode, we saw her use her speedster power to help Barry punch a satellite into dust to save Central City. Did that have something to do with it? Another mystery was also solved — the symbols that Wells was incomprehensibly writing (as well as the season’s most oft-uttered phrase, “This house is bitching!”) were all explained as being a part of this day (or several days), which Barry must have revisited in the Speed Force while he was existing without time. In any case, Mystery Girl solved! Except … where do things go from here?