Season 4, Episode 1: “The Flash Reborn”
In the fourth season premiere, the cliffhanger established the season before is resolved, and Barry is brought out of the speed force. He isn’t entirely himself, but Iris finds a way to get through to him as usual, bringing our favorite hero back to his own mind by the end of the episode. As a treat for fans, a few Easter eggs and foreshadowing hints are peppered through Barry’s post-speed force ramblings. Some of them would come to pay off over the next couple of seasons. At least one key one has not. Yet.
Season 4, Episode 3: “Luck Be a Lady”
Is it strictly necessary to see this episode to follow the show in a binge watch? No. But it is a fun episode. And after the dark and emotionally draining episodes immediately preceding this, it’s nice to have a bit of a break – and some humor – before launching into the rest of the season’s drama.
Season 4, Episode 4: “Elongated Journey into Night”
It would be hard to overstate how reluctant I was to include this episode. Ralph is an important character, who has a large role to play in the remainder of the series and will make regular appearances in subsequent seasons, as well. In later seasons, he’s actually quite likeable and even somewhat endearing at times. He is anything but in this season, so watching episodes like this one can be a bit of a chore. Still, to know who the character is and what he can do, it’s probably important to watch this episode. Or, I don’t know, Google him or something. He does get better later. I promise.
Season 4, Episode 7: “Therefore I Am”
Every season has an episode that explains (or tries to explain) who the villain is and what they’re after. This is DeVoe’s origin story. It’s also the episode where Barry learns the Thinker’s true identity, and Wally finally returns to the team after a hiatus.
Legends of Tomorrow, Season 3, Episode 8: “Crisis on Earth-X, Part 4”
An important episode, in that it’s the one in which Barry Allen and Iris West finally get married. Also an infuriating episode, because neither this wedding nor the wedding between Oliver Queen and Felicity Smoak are handled particularly well. So if you don’t watch it, maybe look up some clips of the Westallen wedding(s) on YouTube or something.
Season 4, Episode 9: “Don’t Run”
Man, Barry and Iris cannot catch a break. First their wedding is invaded by actual Nazis from another Earth. Now Barry is framed for a murder he didn’t commit. On the positive side, this episode showcased why Iris became team leader, and why she was so good at it: she was willing and able to make the choices other characters wouldn’t or couldn’t.
Season 4, Episode 10: “The Trial of the Flash”
I’m an attorney, so I can say that Cecile isn’t a terribly good one when she steps in as Barry’s defense council when he’s framed for murder. Still, this is an important episode, if for no other reason than for the beautiful scene between Barry and Iris when he pulls her into Flashtime. Flashtime will come into play again in one of the best episodes of the entire series, so this episode is a nice introduction to it.
Season 4, Episode 13: “True Colors”
This entry deserves a spot on our list because it’s the episode where Barry is let out of prison, and it establishes DeVoe is targeting a certain group of people in order to steal their powers. As one might expect, it’s an important plot point for the season. Also, in case you’re wondering how far DeVoe is willing to go to get what he wants? The answer is “too far.”
Season 4, Episode 15: “Enter Flashtime”
Just watch this one. It’s quite possibly the best episode of the series. It is certainly one of my favorite episodes of the entire show. Trust me on this. Just watch it.
Season 4, Episode 23: “We Are the Flash”
To be fair, there are a few episodes this season that I haven’t included that focus on Killer Frost and set up her arc for the next season. Most notably, there’s episode 18, “Lose Yourself,” in which Caitlin seemingly loses her powers for good and – after spending a year trying to get rid of them, going so far as to team up with a human trafficker in an attempt to do so – she eventually realizes she wants her powers after all. There’s also episode 20, “Therefore She Is,” which establishes why Killer Frost isn’t like other metas, which should come into play in the next season but doesn’t really end up mattering at all. I don’t mention them because Killer Frost is retconned so much in this show, it’s hard to keep track of who she’s supposed to be and why at any particular moment, and her supposed uniqueness ends up being completely irrelevant in the end. Still, you can watch those episodes to follow her plothole-laden arc. Or you can just skip to this one, and see how Barry finally stops DeVoe for good.