What's Past is Prologue

Synopsis
In the 100th episode, Barry and Team Flash come up with a plan to stop Cicada. However, the plan calls for Barry and Nora to travel back in time to gather some key necessities. However, Barry hesitates, concerned about his daughter seeing certain parts of his life. Meanwhile, Sherloque takes his concerns about Nora to Iris, and Caitlin turns up a key asset in the fight against Cicada.

Trivia

 * The episode's title is a reference to a famous line from the William Shakespeare play The Tempest.
 * At the beginning of the episode when Ralph and Sherloque are sitting in a car snapping pictures of Orlin, Ralph asks how may pictures Sherloque's taken. Sherloque says, "I've shot like a hundred". This may be a nod to the fact that this the is the 100th episode of the series.
 * Sherloque and Thawne compliment Nora as a "clever girl". These were the famous last words of Robert Muldoon from Jurassic Park.
 * Thawne mistakenly refers to Nora as "Dawn", a reference to Dawn Allen, Barry and Iris' daughter in the comics in the original timeline. He also claims that "at least [Barry] still had one." This may be a reference to Barry and Iris having two children in the comics, the Tornado Twins: Dawn and Don Allen. However, in the context of the show, Eobard is more likely referring to how he killed Nora's namesake and Barry's mother, Nora Allen.
 * Furthermore in the comics, Barry's daughter Nora Allen is from an alternate timeline where he married Jessica Cruz/Green Lantern.
 * When Thawne is trying to figure out who Nora is, he guesses the names of three heroes:
 * Jesse Chambers; Thawne is most likely referring to Jesse Chambers Wells/Jesse Quick. Jesse's comic counterpart was named Jesse Bell Chambers.
 * Libby Lawrence; In the comics, she was Jesse Quick's mother and a superheroine known as Liberty Belle.
 * Danica Williams; In the comics, Danica Williams is The Flash of Earth-12, which is based on the DCAU Justice League Beyond tie-in comics following the events of the series Batman Beyond. Danica is from the future and Wally West's successor.
 * Eobard revealed that he somehow knows of Savitar as he has already seen his face to make fun of it.
 * At one point, Gideon was about to say that Nora is the fifth recruit of a rebooted Legion before Barry interrupted her. Similarly in the, Gideon was about to say that Barry is the founder of an organization before he interrupted her.
 * Barry tells Nora why Thawne killed his mother in the context as he was told by the Reverse-Flash in.
 * Ralph plays the Huey Lewis and the News song "Back in Time" as Barry and Nora time travel into the past.
 * The times Barry and Nora traveled to are from the following episodes:
 * Season 3's.
 * Season 2's.
 * Season 1's (also Season 2's  as concurrent events), and  (as well as flashback scenes set during that episode from,  and Season 4's  which were all set during Arrow Season 2's , as the events of each of these flashbacks occurred the night of the particle accelerator explosion.)
 * This is the first episode to feature since, albeit only in a flashback.
 * When Barry and Nora return to the present, Ralph asks, "Did you even go?" (since they returned to the moment they left). Caitlin asked Barry the same thing when he returned to the present after running back in time in.
 * Despite being credited in this episode, LaMonica Garrett only appeared in the opening scene from.
 * That scene was also used in the Supergirl episode, and the Arrow episode . However, it was most likely made for this episode since it was directed by Tom Cavanagh like the rest of the episode.

Goofs

 * When Iris shot Savitar in, he fell lying face up. In this episode when Barry and Nora travel back to that night, Savitar was lying face down after Iris shot him.
 * Cisco breaches Cicada's dagger into outer space, but he's previously stated that he's unable to open breaches reaching into outer space.
 * Although, it's possible that Cisco has honed his powers enough since then that he can now accomplish this feat.
 * However, this seems unlikely given that the injuries inflicted to Cisco's hands by Cicada's dagger have kept him from using his powers to their fullest effect.
 * When Barry and Nora travel back to the events of, Iris checked on Barry after Zoom stole his speed. However, in the original episode, Iris checked on him before that happened.
 * Zoom doesn't appear to recognize that Barry traveled back in time; when alerted to Barry and Nora's presence via their usage of the Speed Force, he didn't ask how Barry had his speed back, which he'd taken from the younger Barry moments earlier. After Barry lost his speed in, he didn't regain his powers until three episodes later in.
 * The timeline is now even more messed up since the Time Wraith that showed up when Nora and Barry went back to the night of May 23, 2017 (Savitar's defeat) to get a shard of Savitar's armor, followed them to the day Zoom stole Barry's speed, the Time Wraith grabbed Zoom when he went after Barry and Nora. Zoom was taken by the Time Wraith at the wrong time; He was originally taken by the Time Wraiths in.
 * This would mean that Zoom never would've killed Barry's father, and by extension, Barry would never create Flashpoint, thereby preventing Savitar from becoming a threat.
 * After Zoom kidnaps Caitlin, Cisco runs and calls out to her. In this episode, he is shown looking from behind a closed door, which wasn't closed during the events of.
 * The episode's official synopsis states that Sherloque takes his concerns about Nora to Iris. In the episode though, he discusses this with Cisco, not Iris.