Barry Allen and the Star Labs team learned that Jay Garrick is Zoom in The Flash season 2's previous episode, which also introduced and later killed off the show's first female speedster, Trajectory.
In episode 16, Cisco vibed when he touched Garrick's helmet and saw Zoom's face in the alternate timeline — and it turned out to be Jay. The upcoming episode of The CW series will find Barry trying to find a way to defeat Zoom. It will also see some time-travel and a blast from the past.
Here are five things to expect in The Flash episode 17 [Spoilers Ahead]
1. Episode 17 is titled, Flash Back, which will air on 29 March at 8pm EST on The CW. In the chapter, "A moment in time gets Barry one step closer to Zoom."
2. In the episode, Barry will be determined to go back to Earth-2 to stop Zoom for good. According to the synopsis, "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 (Tom Cavanagh), to teach him how to run faster." The promotional pictures released show Cavanagh's character in a wheelchair as he was throughout The Flash season 1.
3. Andy Mientus will reprise his role as metahuman Hartley Rathaway aka Pied Piper in episode 17. Although Barry's time travel plan does not go as planned, he will be stunned to face familiar foe Hartley Rathaway. Barry will also meet his old friend Eddie Thawne (guest star Rick Cosnett) in the episode.
4. The episode will find Iris making "peace with her past in order to embrace her future". With her new boss flirting with her, she will probably give love another chance.
5. Episode 17 will air after Flash's appearance in Supergirl. The events of Supergirl-Flash crossover will be referenced on The Flash according to executive producer Greg Berlanti. He told TV Line, the event will be referenced "a little more subtly than we were going to, initially."
Besides, the episodes "kind of flip order" Berlanti says. "We're much better at coordinating the viewing patterns when we're crossing over on the same network. But when [it's folded into The Flash], people will get it," he added.