The 100th episode of The Flash starts with Ralph and Sherloque staking out Orlin Dwyer. The two take several pictures and return to the team at STAR Labs to reveal what they found. The pair
The group starts discussing ways on way to stop Cicada and Nora mentions they need to make a power dampening device. They eventually decide that they need to travel back in time in order to perform a "Time Hack," in which they'd plant an item in the past that they'll need in the future. They agree that they should plant the power-dampening device in the hospital in the past so that they can enter the hospital in the future undetected by Cicada.
Barry and Nora travel through the Speedforce to go back in time to when Barry faced off versus Savitar so that they can take back pieces needed from Savitar's broken suit. After they return, they're soon followed out of the stream by a Time Wraith. Barry agrees to lead the Wraith on a chase while Nora recovers the shard.
The two then travel back in time again to 2016 to retrieve the Speed Force cannister Zoom previously used so that Cisco can use the tech to build the device. The two are stopped by Zoom and lead him on a chase through the Speed Force. Barry and Nora fall out of the Speed Force and Nora eventually convinces her father to stay in the time they fell out in and get help from Eobard Thawne.
After convincing, Thawne agrees to help them fix the Speed Force cannister previously taken. They then go back in time again to the night the particle accelerator was first turned on. They sneak around the basement of STAR Labs when Barry informs his daughter of his past with Thawne. Nora didn't realize that Thawne was responsible for the death of Barry's mother. The particle accelerator goes off and the two use the cannister and fixed tech to make the dampening device. Barry hides it within a pillar at the hospital and the two race back to present day.
Thinking that Cicada's powers are taken away, Barry and team go to the hospital to confront him. They're able to get Cicada's dagger away from him and Cisco vibes it into outer space. The success is short-lived because Cicada recalls the dagger back to Earth and the two sides fight. Before long, Cicada escapes.
The team returns to STAR Labs and Nora realizes her journal is missing. She eventually finds Sherloque reading through it and he finds a passage in a language he doesn't recognize. Nora says she created the language and Sherloque gives the journal back.
Nora leaves and we see that Sherloque was running a translation on his computer and this particular journal entry in question reads "the timeline is malleable." Nora races back in time to watch her grandparents talk from afar. She's watching them when Barry sneaks up behind her. The two watch them for a while before they speed off in a race.
Nora goes to Gideon's room at STAR Labs and has her relay a message to an unseen recipient. When Gideon asks if there's anything else she wants, Nora speeds off into the future. In the year 2049, we see Nora is working with Eobard Thawne.