We open with Nora visiting Thawne to let him know the cure is finished and ready to be used on Cicada, but Thawne confesses that a new timeline is trying to break through and is now unpredictable. He tells Nora she must find Cicada before the timeline officially changes. Nora thinks it’s her fault, but Thawne tells her it’s a new, mysterious variable coming for them.
At Star Labs in current time, Iris is on the phone dealing with the fallout from Grodd vs. King Shark. She and Barry walk in on Nora taking the reigns to try and find Cicada so they can use the cure on him today. Unfortunately, the team hasn’t found any answers. Barry tells Nora to be patient and that he will resurface, but Nora doubts maybe he won’t be ready and quizzes him on what he’s going to say when he gives Dwyer the choice to take the cure. Barry and Iris fake an emergency at Jitters so they can distract her from her overzealousness.
At the CCPD, Cecile visits Joe at his desk. Cecile wants to get her hands on the Cicada task force file, which Joe is already looking through. He asks Cecile about the Doctor who treated Grace and Cicada after the Enlightenment. Joe finds t strange that she’s still treating them even though she’s an ER doctor. They decide to go down and ask her questions.
Down in Jitters, Barry and Iris distract Nora with her own personalized drink. Barry and Iris have made a list of things to do with XS, hoping that they have time to do them with her. They get a real alert of an attacking meta at the college and run to help.
They find a man at the University who can shoot green acid out of his hands. They try and stop him with sodium bicarbonate but he disappears. Nora notices the guy was in the newspaper article Thawne showed her and informs Barry today is the day they stop Cicada.
Back at Star Labs, Nora says that there is a photo of Flash and Cicada in the Flash Museum with a picture of the acid Meta there. Sherloque wonders why she’s explaining it now, but Nora claims usually things are unpredictable, but this time everything is the same.
Everyone goes to do their jobs, but Iris stays behind with Sherloque, noticeably upset that if today is the end of their journey, Nora will have to leave, so she goes to find her. She tries to bond with Nora one more time, but Nora has to leave quickly to go talk to Barry.
Cecile and Joe track the doctor down at the hospital. They start questioning her, and using her empathic abilities, Cecile can tell the Doctor is lying about protecting Cicada and supplying him medicine. Joe lets her go, however, because they don’t have enough evidence. They have an argument over “whose gut to trust.”
Nora and Barry work on how to take down Cicada at Star Labs. Nora thinks Barry’s legacy will help them figure things out. They review some of Barry’s past words to figure out what to say to Dwyer. Barry thinks this time is different, because Cicada doesn’t care if he lives after he’s wiped out all metas, but Nora has faith in him.
Cisco is working on an anti dampening ray to slow down Cicada, and Sherloque feels there’s more mystery to solve before he heads back home. He then reveals he already has found the solution to slowing down Cicada.
We pick up at Cicada hunting down the Acid Master, ready to end up, but it turns out to be Killer Frost in disguise, who stuns Cicada and throws his weapon out of reach. Frost then breaches out Flash appears. He tells Cicada that they have a cure and want him to take it. Barry tells Cicada that he will be remembered as a monster, not a hero if he chooses not to take the cure. Cicada then grabs Flash and throws him on a car, before retrieving his dagger and going to kill Flash, but gets stopped by Frost just in time. He then disappears into the night, and Nora claims that it was their last chance to beat him.
Team Flash tries to find Cicada again but can’t hunt him down. Nora thinks they can find another window of opportunity.
At CCPD, Joe runs into Barry who tells him to keep his head up. Barry confesses he’s worried about what will happen once he finds Cicada again and what he will say. Joe tells him to be less Flash and more Barry Allen—to be more human, and less meta. Barry tells Joe to let Cecile help and do the best job at what she’s good at.
Nora is at the lab desperately trying to figure out what Barry could possibly say to Cicada but Iris wants to take Nora back to Jitters. Iris explains it’s the last time they get to spend together.
Joe meets up with Cecile to apologize. He asks her to join him in the interrogation of The Doctor. The Doctor claims she would never help a vigilante, but Joe and Cecile think that she wants to harm metas like Cicada because of her fiancé who was killed by some. They tell her she can be freed from her guilt if she helps them hunt down Cicada. They ask her to help them set up a meeting so Flash can give him the cure. The Doctor agrees to make contact and share the location, but Joe pushes because Cecile can tell she’s hiding more information.
The secret is that Grace, Cicada’s niece, is also a meta.
The team deals with the new information, assuming that Grace becoming a meta must be new, and it’s the dark matter in her head. Barry thinks they need to take a different approach with no fancy tricks—just Barry talking to Dwyer.
Nora tells Iris about the news and reveals that she also has a list of things she wanted to see with her parents and she understands why Iris is going to miss her. She apologizes for not focusing on her parents when they are the reason she came back to the current time, to begin with.
Flash goes to meet Cicada one more time, wanting to talk. Barry appeals to Cicada through Grace, explaining that Grace is now a meta, and how The Doctor is afraid he’s going to kill her and not be able to come back from it. He asks Cicada if Grace deserves to die. Cicada says no, and also doesn’t want to live in a place where she lives in fear. Barry explains the cure will heal both of them. Cicada is doubtful, so Flash takes off his mask and shows his real faith, explaining that he is a father also, and he loves his daughter more than anything.
Barry brings Cicada back to the labs. Cicada doesn’t understand why they are at the lab, but they have to be sure that the cure is successful and Caitlin will have to help Cicada’s wound, but Cicada only wants The Doctor. Cicada also tells them if they are lying or anything goes wrong he will kill everyone.
Cecile is overcome with Cicada’s rage as he preps to get stitched up, and Cecile has to leave. The rest of the team waits for the results. Caitlin injects the cure into Cicada’s body and his vitals start to spike, and his powers disappear. The doctor stitches up his wounds, but the power in Star Labs shuts off.
Cecile gets a feeling that someone is coming, when a mysterious figure appears, looking like Cicada, and they trap Sherloque, Nora, and Cecile with their powers before storming off.
Without power, Killer Frost stitches Dwyer up with her powers and go after the new villain. Everyone prepares to fight the mysterious figure.
The new figure looks just like Cicada but with two daggers instead of one. Team Flash attacks, but the figure easily thwarts their attacks, injuring almost everyone and then leaving.
The new Cicada finds The Doctor and Dwyer, takes Dwyer's old dagger and stabs The Doctor, killing her.
Everything in Star Labs is down. Everyone is bruised but OK (besides The Doctor).
At Dwyer's house, Dwyer lays unconscious as the new Cicada waits for him to wake. When they take off their mask, it’s revealed to be a future Grace.