'The Flash': Could "Cause and XS" Be Why "Crisis on Infinite Earths" Comes Early?

The Flash tackled time-travel again on tonight's episode, "Cause and XS," and just like usual, things got out of control very quickly.

So out of control, in fact, that it left us wondering what kind of permanent damage Nora Allen has done to the timeline, and whether it could be this episode that precipitates the early onset of "Crisis on Infinite Earths."

Spoilers ahead for "Cause and XS," which aired tonight.

In the final scene of the episode, Nora travels back to 2049, where she demands of Eobard Thawne that she wants to know they are not "making it worse."

It, presumably, being the timeline.

Thawne reassures her that if they can defeat Cicada and take away his knife, then they will be able to alter the timeline and save Barry.

Barry, of course, is expected to disappear and never return during the events of "Crisis on Infinite Earths," which will be next year's Arrowverse crossover event.

The revelation that "Crisis" was coming in 2019 was a surprise to fans of The Flash, since an image depicting the cover of a future issue of the Central City Citizen, dated 2024, has been teasing the Crisis since the series pilot.

With the recent revelation that XS did not come back in time simply to see her father, but rather to save him, it is clear that she is not trying to avoid making changes to history -- something her father lectured her about at the end of this week's episode, using an almost-verbatim speech lifted from Jay Garrick, no less. Rather, she is actively trying to find a loophole that will allow her to prevent the Crisis, or at least change Barry's fate in it.

As a result of her changes to the timeline, Iris founded the Central City Citizen earlier than the masthead had originally suggested, something that they took as a positive sign: the future is malleable!

Of course, while time can be malleable in the Arrowverse, "Cause and XS" reminded us that there are moments in the timeline that are fixed. Those moments cannot be changed -- or if they are changed, it tends to be as a result of great effort and at a cost.

For instance, when the Legends needed the blood of Jesus in season two, someone suggested plotting a course for the Crucifixion, and Rip Hunter immediately put a stop to it, declaring that any changes made to such a moment in history could have profound ripple effects. Barry reiterated that tonight during his conversation with Nora -- and it feels more likely than ever that we will be revisiting that moment as the end of the season nears.

The idea of time that is solid rather than changeable is something that Geoff Johns, executive producer on The Flash, used a lot in his mainstream superhero writing in the 2000s. One example is Booster Gold #5, in which the title hero tries to prove that saving his best friend from being murdered is possible...by setting a slightly lower bar for himself first. He travels back into the events of The Killing Joke to prevent Barbara Gordon from being shot and paralyzed, but fails every time, despite having superior armament to The Joker and his goons as well as knowledge of events that should have helped him succeed. This, it was eventually explained, is because what happened to Barbara was a moment of solid time that could not be altered without catastrophic consequences to the timeline.

It would not be difficult to imagine a season finale that concludes with the realization that whatever Nora and Thawne have been doing has not, in fact, made Barry, or the Earth, or the multiverse, safer -- instead, that it has pushed the Crisis up five years, resulting in the 2019 date.

That may be Thawne's plan since, while he is telling Nora that he is acting in her interest, he is still Barry's greatest enemy and the idea of him helping ot save Barry's life raises all kinds of questions.

Given that we do not know exactly how old Nora is or how old she was when Barry went missing in the Crisis, it is also possible that Nora herself might cease to exist when the Crisis moves back to 2019, as it is possible that Barry will now have disappeared before she was conceived.

In any event, as the season progresses it seems more and more likely that Nora will be exacerbating the damage she has done to the timeline, not just with her mere presence, but with the aggravating factors of 53 trips back to the previous hour in "Cause and XS."

The question then becomes whether Thawne will be a help or a hindrance in the Crisis...and whether all of the Flash family can survive it.

The Flash airs Monday nights at 8 p.m. ET/PT, before episodes of Roswell New Mexico on The CW.