When "The Flash," last aired, Team Flash had just defeated King Shark, they had successfully closed the breaches to Earth-2, and they were faced with the shocking death of Jay Garrick. While viewers at home were left to deal with Jay's death, they also got to see Zoom take off his mask, which surprisingly revealed the face of Jay Garrick. This week the show picked up a few weeks after those final moments, with Barry training to become faster than Zoom again. Jesse Quick got to do some exploring this week, Iris went on a "date" with her new boss Scott Evans, and a new speedster was in town, "The Flash's" first female speedster, Trajectory.
Trajectory was quite a surprise in this episode. When she raced into the club where Barry (Grant Gustin,) Iris (Candice Patton,) Wally (Keiynan Lonsdale,) Caitlin (Danielle Panabaker,) Cisco (Carlos Valdes,) and Jesse (Violett Beane) were enjoying a night off, everyone thought she was The Flash. She stole hundreds of dollars out of people's wallets in the blink of an eye, leaving a similar trail of yellow and red lighting behind her. How could she not be The Flash? Barry was able to track her down, but he was only fast enough to see her face. She was by far much faster than he was, and everyone on his team was impressed to know she was a girl. But her presence in Central City raised a lot of questions. Was she a speedster from Earth-2? The team concluded that since they closed all the breaches, she must have gotten her speed from somewhere on their Earth. Caitlin remembered that she shared some of the Velocity-9 information with a former colleague at Mercury Labs, Eliza Harmon (Allison Paige.) When they visited Eliza she denied their allegations, but once Caitlin and Joe (Jesse L. Martin) had left, her dark side came out, and she revealed herself to be the Velocity-9 junkie speedster, who called herself Trajectory.
Up until this point, Caitlin and Wells (Tom Cavanagh) had been keeping Velocity-9 a secret from Barry. Tonight Barry was told the truth and he was furious that his friends would lie to him about the existence of speed-enhancing serum. Barry was intent on using the Velocity-9, but Caitlin warned him that it was killing Jay (Teddy Sears) and that it would be deadly if Barry were to use it. He crushed the last vial, but was still upset that it couldn't help him. This piece of information was key to the team figuring out Jay's connection with Zoom later on in the episode.
When Eliza was out of her last supply of V-9, she broke into S.T.A.R. Labs and threatened to kill Jesse if Team Flash didn't make her more. They complied, but not before Eliza injected Jesse with a near-lethal dose of V-9. Barry went after her and was able to stop her, but not before she could inject more V-9 into her system. Eliza was addicted to the serum, which begs the question, was Jay addicted too? Is that what turned him into Zoom? As Eliza raced away her lightning turned blue, like Zoom's, and then out of nowhere, her cells deconstructed and she vanished into thin air, leaving only her empty suit behind her.
This revelation stunned Barry, and when he told Team Flash, they all came up with the same conclusion: Zoom's blue lightning is a result of cellular degeneration, and he wants Barry's speed, so he can survive. The team also realized that the only other person they knew with the same type of degeneration with Jay Garrick, who was suffering cellular death from an overuse of V-9. This put the whole situation in perspective for the team who, even though they didn't want to believe it, they couldn't help but see the similarities between Zoom and Jay. By using Jay's metal helmet from Earth-2 Cisco was able to vibe, and he saw what we all saw in the last episode of "The Flash," Zoom unmasked as Jay Garrick. This was devastating news for everyone on the team, especially Caitlin, but Barry was affected the most, because that would mean he was duped, betrayed, and lied to by another speedster pretending to be his friend.
The episode concluded with Jesse Quick deciding to leave Central City for a while to get away from her dad and become her own person. After she discovered that he killed Turtle and gave Eliza the V-9 to keep her safe, she knew she couldn't trust him anymore. Iris and her boss, Scott Evans (Tone Bell) mended their relationship, and Iris agreed to go on a real date with him. They were even able to come to an "agree to disagree" arrangement about the inherent goodness of superheroes like The Flash. Barry was able to make an incredibly long jump at mach 3 this week, but that personal victory didn't last long after he found out about Jay.
Next week on "The Flash" Barry travels back in time to question the former Harrison Wells/Eobard Thawne about becoming faster. The timeline begins to suffer deadly consequences and Barry must fix everything before his future is permanently changed. "After the shocking revelation that Zoom is Jay Garrick, Barry is more determined than ever to get back to Earth-2 to stop Zoom forever. Desperate to find a way to increase his speed, Barry decides to travel back in time and masquerade as his earlier self in order to get his arch-nemesis, Dr. Harrison Wells/Eobard Thawne, to teach him how to run faster. However, things don't go as planned and Barry is stunned to face familiar foe Hartley Rathaway (guest star Andy Mientus), as well as old friend Eddie Thawne (guest star Rick Cosnett). Iris makes peace with her past in order to embrace her future."