'The Flash': Breaking Down the Ending of "What's Past is Prologue"

Tonight The Flash aired its landmark 100th episode and while it was an episode that packed in a lot of well-placed references to the seasons leading up to tonight, it's the ending that may leave fans talking for quite some time.

Spoilers for tonight's episode of The Flash, "What's Past is Prologue", below.

Tonight, Barry and Nora raced to different points in the past to assemble the objects needed to create a device that would disable Cicada's dagger and allow them to apprehend the mutant serial killer. After a few tense and bumpy moments in the past -- as well as a whole lot of revelations about Barry for Nora -- the pair was successful with the device. Unfortunately, the plan didn't quite work the way it was intended and despite their best efforts, Cicada was able to regain his dagger and get away.

That alone would have been a solid episode ending, but "What's Past is Prologue" isn't an ordinary episode. It's the midseason finale so the show went a little further. First, the episode revealed that Nora's mysterious writing in her journal is some sort of Time Language allowing her to note events in a lasting way without losing them when the timeline changes. We also discover that Sherloque had translated some of her writing to say that "the timeline is malleable".

But that language? It's more than just notes for Nora. She's scanning her pages via Gideon and sending them to someone in the future: Eobard Thawne. In the last moments of the episode, we see Nora race to the year 2049 where she goes to confront Thawne who appears to be in prison -- presumably over the fact that he withheld the bit about how he murdered her grandmother -- but Thawne is glad she's there. They need to talk.

What? Nora's been working with Thawne? What is happening here? The clue may itself lie in the date Nora ran to: 2049. If you remember from the series premiere, that would be the date of the newspaper reporting on the 25th anniversary of the mysterious crisis that Barry Allen disappeared in. One of the interesting notations in that newspaper article? Reverse Flash (aka Eobard Thawne) was there -- and may have been involved.

"But in the years following the crisis, accounts only grew more contradictory. Some eyewitnesses remember dozens of other heroes present, including Green Arrow, Batwoman, and Elongated Man. Others remember heroes thought lost in time, like The Atom, or from other worlds, like Supergirl. Some even contend they saw Reverse Flash leading an army of "shadow demons.'"

So, what does this mean? This whole season has been centered around Nora wanting to spend time with her father as he never returns, but it now seems like the real reason Nora's in the past is to try to stop the crisis from ever happening and, somehow, she's allied herself with one of the few figures present when he vanished to do so. But, as fans of The Flash know, you can't really trust Eobard Thawne, so it will be very interesting to see how this all plays out, especially with "Elseworlds" kicking off in just a few short days.

What did you think of tonight's episode of The Flash? Let us know in the comments!