Barry finds himself fighting a misty meta-human, who's out for revenge against those who got him arrested and executed.
- Ambiguous Ending: During Wells' flashback to the accelerator explosion Wells is shown to be expecting Barry getting struck by lightning but its left unclear whether or not he caused the explosion.
- Anti-Climax: Discussed. Wells turns on the reactor with the touch of a screen and very little fanfare. The scientists joke about how they expect more.
- Big Eater:Barry: [just getting back from stopping a criminal] You wanna grab a bite? I'm feeling a little...famished.
Iris: After the Mongolian barbecue we had before the movie, and the extra-large popcorn you had at the movie? How are you not...fat?
Barry: I've been jogging.
Iris: Oh, okay.
- Blessed with Suck: Barry's advanced metabolism is revealed to make anesthetic useless, meaning he's going to feel the full pain of every injury from now on.
- Chekhov's Gun: The hidden cameras installed in Barry's lab at CCPD that was revealed in The Stinger becomes important near the end of the season.
- Clark Kenting: Averted. Barry knows his father will recognize him even with the mask on, so he blurs his face.
- Dude, Where's My Respect?: Barry is irritated by a pair of cops taking complete credit for catching a guy he hand-delivered into the back of their car.
- Everyone Knew Already: Well, more like the one person that it was supposed to be secret to, knew already:Joe: (to Iris and Eddie) You two arrive at the same time?
Iris: Dad, we have something, uhm, that we need to tell you... (Joe gives her an awaiting look) Dad, the thing is—
Joe: (in a matter-of-fact manner) You two are dating. I know.
Iris: You do?
Joe: I'm a detective, remember? ...And both of you're lousy lairs.
Eddie: (relived) So, you're not mad?
Joe: (serene) Oh, I'm mad. If the doctor hadn't confiscated my gun, we'd be having an entirely different conversation.
- Harrison Wells comments that it feels like he's been waiting for centuries for the activation of the particle accelerator. Later episodes confirm what had as of this point only been implied by episode stingers: Wells is from the future, casting his words in a whole different light.
- The fact that there are hidden cameras in Barry's lab at CCPD.
- Good Thing You Can Heal: Barry survives Mist attacking him because his Healing Factor continually regenerates his lung cells as they're killed.
- Heroic Sacrifice: Ronnie asks Cisco to initiate lockdown and refuses to let him open the doors (and locking him inside the reactor) so that the blast can be contained.
- Hoist by His Own Petard: The mob group at the start of the episode. The Boss had bulletproof glass installed just in case. Said glass proves their end when his nephew can't shoot it out and vent the room. Of course, that would only have worked on a regular gas attack, rather than a being of living gas...
- I Should Have Been Better: Barry says this almost verbatim about failing to save one of Mist's victims.
- Irony: Of the humorous sort. Iris claims to be sure the "streak" is a man, because she's intuitive about these things. Barry just smiles.
- Killed Mid-Sentence: Ronnie who dies in the middle of a goodbye to Caitlin
- Mundane Utility: It's implied that Barry works up a fiber analysis at super speed, though he may have just run upstairs and grabbed it off his desk. At super speed.
- Mythology Gag:
- The cinema is playing Blue Devil II - Hell to Pay and The Rita Farr Story.
- Barry comments that he wouldn't want a museum built in his name. In the comics, there is a Flash museum.
- Ronnie used to say that he and Caitlin were "like fire and ice". In the comics they literally are, as Firestorm and Killer Frost, respectively.
- DC's standard Arc Number, 52, is brought up again, this time being the number of minutes it apparently took the jury to find Barry's father guilty.
- A sign with 52 on it can repeatedly be seen in the background at S.T.A.R. Labs.
- In-universe, Wells tells Barry that the North Wing of the mall is the one with the Big Belly Burger, a which was a meeting place for Team Arrow in Arrow season 1.
- Nice Job Breaking It, Hero!: Discussed and narrowly averted. Joe discourages Barry from releasing Henry from the jail, because it will force him to be a fugitive forever, which can hardly be called a good life.
- Overprotective Dad: Joe jokingly threatens to shoot Eddie for dating Iris.
- Police Code for Everything:Barry: Hello?
Cisco: Code 237 on Wade Boulevard.
Barry: Public indecency?
Cisco: Wait, I think I meant a 239.
Barry: Dog leash violation?
Caitlin: Bad man. With a gun. In a get-away car. Go!
- When Barry comments about a real-life zombie phenomenon that can be found on fungus-infected ants, this is also how the video game The Last of Us was inspired.
- Barry runs to stop a crime on "Waid Avenue". This is a nod to veteran Flash writer Mark Waid.
- Unconfirmed and possibly a coincidence, but Caitlin and Ronnie plan on going to Tahiti on their honeymoon. Anyone who watches Marvel's Agents of S.H.I.E.L.D. knows that Tahiti is a magical place.
- Super Smoke: Kyle Nimbus has the power to willingly turn into a cloud of poisonous gas and retain movement control. While under this shape he can also move about as fast as the Flash, but it is exhausting and he's soon forced to return to his human form.
- Tailor-Made Prison: The particle accelerator gets adapted as a special makeshift prison to hold metahumans, with Mist as the first inmate. Wells and Cisco also comment on how they'll modify each cell accordingly with the prisoner's abilities.
- What You Are in the Dark: Barry could break his dad out of prison using his powers. In the end, he decides to try to prove his dad's innocence instead.
- You Did Everything You Could: In response to Barry's I Should Have Been Better Joe tells him that he has limits despite his powers and that he can't save everyone.
- You Won't Feel a Thing: When Mist attacks Barry in his gaseous form. Barry uses his trademark quick thinking and doubles back to S.T.A.R. labs, so a sample of Mist can be taken directly from his lungs. The problem is that Barry's superhuman metabolism renders the use of anesthetic void. Cisco, nonetheless, tries to reassure him that it won't be too big a problem:Caitlin: Cisco, give the syringe. (to Barry) This is gonna hurt a lot!
Cisco: (grabs a syringe with a needle that could charitably be called "medium" sized) It's a small needle. You probably won't even feel it...
Caitlin: ...You're definitely going to feel it.