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"The ripples you'll cause, who's life you're gonna affect. No one can do that."
"No one?"
"No. We're not gods, Nora. We've just been given extraordinary abilities.
Barry Allen and Nora West-Allen

"Cause and XS" is the fourteenth episode of the fifth season of The Flash, and the one-hundred-sixth episode overall. It aired on February 12, 2019.



Cisco has finished the metahuman cure, but he says it's going to take 29 days for it to be ready. The team is unwilling to wait that long, as Cicada can go on a rampage before that. They discover that to polish it off, Barry needs to bring it into the Speed Force, reducing the 29 days to one hour. Nora wants to go with him, but Barry denies it, and leaves XS to protect the city. After Barry leaves, Ralph appears with his "Book of Ralph" with the intention of preparing Cisco for his date with Kamilla. Nobody stays in the Labs to help him, except Nora. Cisco goes on his date by taking pictures about what kind of men Kamilla is supposedly into according to Ralph's research.

Cisco appears on the date in Jitters, wearing a fancy suit, which is clearly an overdress. He tries to act like some businessman (like he was during Flashpoint), but the date turns awkward. Meanwhile, Iris is in her office working, when Cicada suddenly appears, and takes her captive. She manages to trigger her alarm, alerting Nora and Killer Frost to her location. However, Cicada is waiting for them, and throws his dagger, which hits and kills Frost. Realizing she can't beat Cicada, she runs back in time by one hour, appearing in S.T.A.R. Labs at the moment Ralph appears.

Intending to prevent, what happened, Nora convinces Iris to remain in S.T.A.R. Labs, but she won't reveal why. Cisco goes on his date, this time dressing like a bodybuilder. But he starts to have vibes about the previous cycle. Meanwhile, Cicada appears again in Iris' office, but this time, Ralph is in his neighboring office and tries to stretch his arm to grab an ale bottle, but Cicada's dagger takes away his powers, and the bottle shatters. Cicada hears this, and grabs Ralph. Like Iris last time, Ralph manages to alert for help. Nora goes with Frost again, and pushes her out of the dagger's way, but the dagger kills Ralph this time. Running again back in time, Nora ends up in the same moment like before.

Next, Nora tries to keep Iris, Caitlin and Ralph in S.T.A.R. Labs. Suspicious, Sherloque goes to Iris' office to find out, why Nora doesn't want Iris to go there, and as he is captured by Cicada, he realizes it's because Nora travels back in time. Cisco is in his date again, getting vibes about his previous dates on the last two cycles. As Sherloque's alarm goes off, Nora goes again to the rescue, but Cisco breaches there first, and is killed. Nora reverses time again to the same moment. In order to get advice from Barry, Nora attempts to run into the Speed Force, but she ends up again in the same moment and here it becomes apparent she is stuck in a time loop.

To make sure none will be killed, Nora has everyone remain in S.T.A.R. Labs. But this time, Cicada goes to Iris' office and learns about Cecile. Her alarm goes off, and as Nora tries to save her, she is killed. Following this, Nora resets time multiple times, but every time someone is killed.

After 52 attempts, and the fact that Cisco has been getting vibes about the previous cycles, Team Flash realizes Nora is reversing time. Nora explains, that no matter what she does, someone will die in each cycle, even though she has been writing notes from each cycle in order to prevent anyone from dying. Overwhelmed, that she can't seem to fix this, she goes to the pipeline to think. Cisco arrives, and explains that he has experienced similar situation once before, when Eobard Thawne killed him, but Barry reset the timeline then[1]. He still kept having vibes about it. However, all this has made Cisco realize he just needs to be himself with Kamilla. Nora then finally realizes, how she can break the loop, and the team comes up with plan to stop Cicada by having the dagger hit him, but in order for it to work, Nora needs to be slowed down, so that she can reverse time a little.

The plan is set, and Iris acts as the bait. Cicada throws the dagger, and Cisco, Frost and Ralph come from a breach and attack him, while Nora reverses time just as the dagger is about to hit Ralph. The plan succeeds, and Cicada is hit by the dagger. He flees.

Back in S.T.A.R. Labs, Barry returns with a prepared cure, and he learns what happened. Cisco goes to to his date as himself, and this time, things go smoothly. Nora explains to Barry, what she did, and Barry then explains to Nora about the consequences of time travel the same way Jay Garrick explained to him, after he undid Flashpoint.



Guest starring[]



  • The episode's title is a play on the phrase "cause and effect". This is also a season three episode titled "Cause and Effect".
    • This episode also has a very similar premise to a Season 5 episode of Star Trek: The Next Generation, called "Cause and Effect", in which the crew try to escape a time-loop where the Enterprise is destroyed every time.
  • This is the first episode of The Flash in which Grant Gustin doesn't have a lead role.
  • Nora resets the timeline 52 times (53 if the timeline where none of Team Flash are killed counted), a reference to the famous DC number 52.
    • Another reference to 52 is that the alert broadcast almost always goes off at 8:52 PM.
  • Of the multiple timelines, the first time that a character (Nora) notices the time as 8:07 PM lined up exactly with the broadcast time at that moment. The other two important times, 8:27 and 8:52 didn’t line up with "real time" 8:27 came closest, but was two minutes off.
  • Cisco states that giving the cure to Cicada in a month would be very fast for them to stop a "big bad". This is a fourth-wall reference to the fact that it's always taken a full season for Team Flash to defeat each main antagonist.
  • Barry teaches Nora about time travel, using the example of a coffee cup being like the space-time continuum, breaking whenever you travel through time, directly quoting what Jay Garrick had told him about the consequences of time travel in "Paradox"​.
  • The animation when Nora runs back in time is somewhat similar to the animation of Earth-90's Barry Allen when he time traveled in his version of The Flash​​​.
  • Cisco mentions Sun Tzu to Ralph Dibny, who is a Chinese general, military strategist, writer, and philosopher who lived in the Eastern Zhou period of ancient China, best known for writing The Art of War.
  • The events of this episode are very similar to the events of the DC's Legends of Tomorrow​​​ episode "Here I Go Again"​​, in which Zari Tomaz is stuck in a simulation of a time loop, reliving the same hour over and over again with the Waverider exploding at the end of each loop. Here, Nora ends up being able to run only one hour into the past to keep anybody on Team Flash from getting killed by Cicada.
    • In addition, in "Here I Go Again", before Zari realizes she's stuck in a time loop, she feels as if she's experiencing déjà vu. In this episode, due to the fact that his powers allow him to remember things that have happened to him in erased timelines, Cisco gets the feeling that he's having déjà vu.
    • Furthermore, in "King Shark vs. Gorilla Grodd", the next episode, Joe describes what happened here (with Cicada kidnapping different members of Team Flash, where someone always gets killed) as a time loop.
  • The first time that Cisco goes on his date with Kamilla (before Nora resets the timeline for the first time), he claims that the company he works for is called Ramon Industries, a reference to the company he owned in the Flashpoint timeline.
  • It's revealed that Kid Flash and Cicada both have drinks served at CC Jitters named after them.
    • However, a deleted scene from the season 3 episode "Duet" had also featured the Kid Flash drink from CC Jitters.
    • In all of the instances where Cisco goes on his date with Kamilla, a man named Ian orders a Cicada, but in the last iteration of the timeline (where none of Team Flash gets killed), a man named Stephan is there instead, who orders a Kid Flash. Moreover, the barista mispronounces both of their names, only to be corrected by the customer.
      • However, this may be due to Cisco going to Jitters at a later time (he went before fighting Cicada, or didn't go at all, in every erased timeline but went after the fight in the current timeline).
  • When speaking with Nora about one iteration of the timeline where he was killed by Cicada's dagger, Cisco mentions the alternate timeline where he was murdered by Eobard Thawne before it was reset by Barry and undone, as depicted in the season 1 episodes "Out of Time" and "Rogue Time".