“Flash Back” is episode seventeen of season two of The Flash.
In the previous episode, “Trajectory”, before Eliza Harmon – Trajectory – ran herself out of existence, her lightning turned blue. Just like Zoom’s. Trajectory was using Velocity-9 to give her speed – she wasn’t a ‘natural’ speedster – so it was presumed that Zoom had used V9 as well. Which lead Wells to conjecture that Zoom was dying, and that was the reason why he wanted Barry’s speed. Jay was already known to be dying from the effects of Velocity, which led them to a conclusion. So Cisco vibed Jay’s helmet and confirmed that Jay Garrick was Zoom.
Barry is reading at superspeed and saying that he let it happen again. He trusted someone he shouldn’t. Just like he did with Wells – the Eobard Thawne version. He made the same mistake twice admittedly with different people) Barry thought that Jay, just like he did Wells/Thawne, was training him how to get faster to help Barry, but, again just like Wells/Thawne, Jay was doing it just to use Barry. Barry wants to figure out how to improve his speed so he can stop Zoom.
Cisco enters the room where Barry is working at S.T.A.R. Labs, sees Jay’s helmet and vibes off it. He asks Barry why he is keeping the helmet around. Barry says it helps motivate him; Cisco says it’s giving him daymares. Cisco has brought Barry every book that is remotely related to speed. Caitlin arrives and says she’s found something interesting. Cisco wants to know whether it’s good interesting or bad interesting. Caitlin has been comparing data on Barry, Zoom and Reverse-Flash. She says that all three are moving their legs at the same speed. Just with each stride, Zoom and Reverse-Flash’s feet are spending less time on the ground, propelling them forward much faster. Barry says he needs to make up the difference somehow; Caitlin asks what if the reason Barry can’t go any faster is because he just can’t.
Later, Joe tells Barry that he should have known better too about Jay, after Thawne/Wells the previous year. He should have dug deeper, but didn’t. When Joe goes to the kitchen, Iris tells Barry that she kind of went on a date with Scott Evans, her new editor. It made her think about Eddie, and she thinks of him every day.
Wally arrives just as Joe brings in the food. He says his advisor loved his engineering design, and wants Wally to work with her. Wally says that he is trying to push the speed limits using smaller engine systems. He reads the journals of famous engineers, ones he can’t talk to in real life because, well, they’re dead. This gives Barry a brainwave, and he makes his excuses and leaves, thanking Wally as he leaves. Who comments that Barry gets weirder every time.
Barry’s idea is to have Eobard Thawne teach him how to go faster, because Reverse-Flash went faster without using V9. So Barry plans to run back in time to speak to Thawne. Barry asks Caitlin and Cisco what they think; Wells, who has just returned after failing to find Jesse (after finding out what her father was willing to do to protect her, Jesse decided she needed some time apart) says that it’s asinine. There are so many ways that Barry could screw things up. Thawne – Wells really doesn’t like Thawne being called Wells, with good reason – spent 15 years studying Barry, and there is a good chance he will know it’s not the right Barry. If Thawne figures Barry out, the timeline could be altered and things will be different when Barry returns – and only Barry will know. Wells says Barry is risking everyone. Barry replies that if Zoom gets Barry’s speed before he figures out how to stop him, everyone will be in danger anyway.
Caitlin and Cisco suggest Barry go back to when everyone was distracted by Hartley Rathaway in “The Sound and the Fury”. That was when they found out that Thawne/Wells could have known about the accelerator explosion, and that they were all angry with him. So if Thawne notices anything off about Barry, he will put it down to anger. Caitlin gives Barry a tranquiliser dart to use ion himself, so he can substitute for previous-Barry. And that Barry cannot tell anyone the truth about Thawne/Wells. Cisco tells Barry to come back to this moment. Otherwise he could end up in a 12 Monkeys timeloop he can never get out. So, no pressure. Barry says ‘What could go wrong?’ in reply. Really? Never, ever say that!
Barry runs back through time, briefly glimpsing something odd as he does, and arrives as his former self is confronting Hartley. He has already come back too early. So, things have already started to go wrong. There is some interference in the comms systems and previous-Barry appears to see future-Barry. Because he did. So Barry and to fight himself in order to dose his former self with the tranq. When Barry defeats Hartley, he brings him back to the lab. Then suggest that Cisco scan Hartley’s ear implants, which Hartley used to break out of his cell before. Barry has already changed things.
Eddie is at the CCPD with Joe, talking about moving in with Iris, and how it is new and exciting. Joe replies that it’s new, but not exciting. Eddie replies that he keeps forgetting Joe is Iris’s father. Joe urges him to try to remember. For both their sakes. He also wants Eddie to look into Wells, off the books.
In Barry’s lab at the precinct, and officer brings a file in then notices that the map of Central City is fluttering. He lifts the poster and the apparition Barry saw briefly appears. It looks like a very dead half a corpse that trails black smoke. And flies. at S.T.A.R. Labs, Thawne gets an alert and tells Barry he needs to go. Barry – who is currently working on the speed equation with Thawne – says the police can handle it. Thawne says they can’t. And they can’t. The floating things isn’t harming any of the police, but it can fly through walls, so it’s no surprise that it proves immune to bullets. When Barry arrives, he sees Eddie, which is a bit of a shock and results in him acting oddly around him. The only damage the immaterial wraith has done is to Barry’s lab, which is trashed.
Thawne is no more an idiot than the Wells he replaced. He’s also got a lot more experience with time travel than Barry, So it’s no great surprise when things start going wrong. Then badly wrong. Barry has already changed the past, in whatever minor way; what effect will this have on the future?