We open with Iris confronting Barry about taking Nora back to the future. Barry says they can’t trust her but Iris reminds him that her feelings are just as important. Barry is insistent that working with Thawne deems her absolutely untrustworthy.
We move to the future where Nora is venting to Thawne about her mistakes, and Thawne apologizes for letting her down. Nora realizes Barry never felt Thawne running to and from the future and asks how he made it possible. Thawne explains instead of using the speed force to tap into his powers, he created his own. Thawne tells her she can access it herself to go back in time. Nora asks him to teach her how.
We jump back to the present at Star Labs. Barry tells the team he took Nora home to the future. Ralph decides to go round up some Cicada files to do research, while Caitlin stays behind with Barry and Joe. Joe gets a call from CCPD about a problem.
At the hospital, Joe and Barry realize that Present!Grace has been kidnapped by Future!Grace. They wonder if things can get any worse (they can always get worse!).
Caitlin's mom Dr. Tanhouser is working late at her lab. Icicle appears, killing a security guard. He breaks into the secured portion of the lab and takes a blue artifact before promptly leaving.
Barry and Joe head to the lab to try and figure out why Icicle returned and stole what he stole. Caitlin arrives and argues with her mother about lying to her about her father for 20 years.
At the West house, Cecile and Ralph discuss why they can’t seem to figure out how to track down Future!Grace. Ralph walks over and notices Iris writing an email about how she can’t forgive Barry. Cecile tells her the only way they are going to solve the problem is together. Iris agrees and heads out the door. Cecile realizes through her empathy how hurt Iris is, and tells Ralph to go after her; she senses her determination.
Iris heads to Star Labs to find a way to get to Nora. Ralph surprises her and tells her he’s going with her.
In the future, Thawne is teaching Nora how to tap into his personal speed force. It turns out his force is spawned from sadness and loneliness; it’s a negative force. Nora fails.
Ralph and Iris work on finding a way to Nora. They open a time breech and jump through.
At the lab, Caitlin explains the particle Icicle took will help him plunge Central City into a new Ice Age. Caitlin thinks she can figure a way to fix it, but her mother has a different opinion on what to do.
Icicle suddenly appears and knocks both Flash and Joe out, then heads for Caitlin and her mother.
At Star Labs, Sherloque prepares to leave Team Flash and go home. At the last minute, he sees the screens alerting him Barry is in danger and breeches to him. Barry is suffering from hypothermia. Sherloque uses current from two cables to shock him back to life. Barry wakes up and immediately tries to go after Caitlin and Icicle, but Sherloque and Joe insist he needs rest.
Caitlin and her mom are at another decommissioned Tanhouser site. Caitlin wants to break from her cuffs and become Killer Frost,w while her mother wants to figure out how to break down eh door. Caitlin confronts her mom about why she’s always been cold and distant,w wondering what she did to get treated so badly. Her mother reveals she was hurt that Caitlin left her.
Icicle enters and takes a blood sample from Caitlin and claims he will see the “Snow Pack” soon. They realize he’s trying to recreate the process so Caitlin's mother can also create a snow personality. Icicle wants to repress their human sides indefinitely.
Iris and Ralph devise a plan to find Thawne. Ralph tries to get through the Warden but gets turned down immediately. Ralph then turns himself into the Warden to get through. Iris walks in on Thawne and Nora talking about how she is too light to use his negative force to go back in time.
Nora explains how crushed she was that Barry left her and ends up tapping into the negative speed force. Before Iris can catch her, she’s gone. When she starts to turn, her light turns from purple and yellow to purple and red.
Thawne tells Iris that Nora is gone, and she’s probably back in 2019. He tells Iris that Nora needs her family. He reminds her they have to stay together and Iris can’t leave Barry like he left Nora. Ralph comes in and tells iris they have to go.
Back with the Snow Park, Caitlin and her mom bond, and talk about Killer Frost. Icicle returns and takes Caitlin's mom away.
Barry is spiraling at Star Labs over not being able to find Icicle and Caitlin without Cisco. Sherloque thinks Icicle is masking himself in a place that is already cold.
At the Tanhouser site, Icicle begins his process to turn Caitlins mom into another frost persona. Caitlin then appears as Killer Frost and knocks Icicle down. Icicle forces Frost to make a choice—save her mother or catch him. Flash finally appears, and Killer Fost tells him to save her mother while she catches her dad.
A chase ensues, while Flash tries to rescue Caitlins mom. Back int he labs, Sherlqoue and West are trying to find a way to help when Iris and Ralph appear to help. Sherloque tells him to phase through the chamber and grab Caitlin's mom so he won’t freeze to death. Because of this, Flash is able to save her life.
The pursuit continues between Icicle and Forst. Icicle stabs Frost and she turns back into Caitlin. Icicle's about to kill her when he touches her heart and melts himself back to his human version.
Grace then appears out of nowhere and starts attacking Flash, knocking him out completely. Caitlin turns back into Killer Frost and they start to battle. Grace is able to take Killer Frost down. Grace throws her dagger, but Mr. Snow jumps in the way to save his daughter. He ends up dying, but not before reminding them that “family should never leave family.”
Back at Star Labs, the team reconvenes. They figure out Grace must have been there for the same particle Icicle wanted, but they aren’t sure why.
It is revealed Caitlins mother is unknowingly still a meta from the time she spent in the chamber.
At the West Allen loft, Barry and Iris talk through their issues. Iris believes Nora is bad somewhere in the present. Barry admits he was wrong for leaving Nora and making decisions without Iris. They agree everything should be decided together as a family. Iris confesses she thinks Thawne might actually care about Nora.
Nora arrives in the present, with glowing red eyes.
At Graces house, Future!Grace takes care of Present!Grace while she’s in her coma.