- Grant Gustin as Barry Allen/The Flash
- Candice Patton as Iris West
- Danielle Panabaker as Dr. Caitlin Snow
- Carlos Valdes as Cisco Ramon/Vibe
- Keiynan Lonsdale as Wally West
- Tom Cavanagh as Dr. Harry Wells
- Jesse L. Martin as Detective Joe West
- Teddy Sears as Hunter Zolomon/The Flash/Zoom
- Violett Beane as Jesse Wells
- Michelle Harrison as Nora Allen
- John Wesley Shipp as Henry Allen and Jay Garrick/The Flash
- Gary Hetherington as Man
Having just witnessed Hunter kill Barry's father in front of him, Barry is sent into a blind rage. Barry chases after Zoom, now faster than him, and is able to beat him up. However Zoom manages to create a time remnant, which is what Barry ends up catching instead. While Barry is moments away from killing Zoom's time remnant, the real Zoom appears and kills the remnant himself.
After Henry's funeral, Hunter challenges Barry to a race to determine who is faster, threatening to kill everyone Barry loves if he refuses. Harry discovers Hunter is in possession of a Magnetar, a device that will destroy every planet in the Multiverse except Earth-1 which requires both their speeds to power. When Barry refuses to back out, the team locks him in the pipeline and forces Hunter back to Earth-2 themselves; but Hunter abducts Joe in the process. Wally discovers this and frees Barry, who agrees to Hunter's race. As Barry and Hunter race around the Magnetar, the former creates a time remnant to free Joe and destroy the machine, but at the cost of dying while the prime Barry defeats Hunter, who is then taken away by Time Wraiths for his crimes against the timeline.
Barry rescues the man in the iron mask, who is revealed to be the real Jay Garrick, Henry's Earth-3 doppelganger. Harry, Jesse and Jay return to Earth-2, from where Jay plans to return to Earth-3. Barry, still feeling broken and defeated, travels back in time and stops Eobard Thawne from killing Nora.
- Cisco refers to his Vibes of Earth-2 being destroyed as like "watching Transformers in 4D", but more realistic and with better acting.
- Discussing Zoom's plan, Cisco states "one pulse to destroy them all", likely a reference to the infamous phrase "One ring to rule them all" from J.R.R. Tolkien's The Lord of the Rings.
- Hunter Zolomon comments on how he'll have "a Flash from two worlds" to keep him company. This is a reference to "The Flash of Two Worlds" story, which featured the Barry Allen and Jay Garrick Flashes crossing over for the first time. Interestingly, this is also the name of an episode earlier in the season, with both Hunter (masquerading as "Jay Garrick" and the Flash of Earth-2) and Barry teaming up to stop Sand Demon.
- Cisco mentions that Harry will do his "best Frankenstein", referring to the titular scientist of Mary Shelley's 1818 novel, Frankenstein.
- The way Barry's time remnant dies is similar to how Barry died during the Crisis on Infinite Earths event, running so fast he disintegrates while saving the multiverse from destruction by the Anti-Monitor.
- When Zoom is pulled into the portal by the Time Wraiths, his appearance resembles that of the pre-New 52 Black Flash.
- This episode picks up immediately where the events of the previous episode left off.
- This episode is the last time that Barry and Team Flash are in the original present day, before the aberration of the Flashpoint timeline and the events of "".
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