When a nuclear bomb threatens Central City, Barry, Jay Garrick and Jesse Quick will have to enter into the otherworldly state known as Flashtime in order to slow things down enough to deal with the crisis.
The Flash comics of John Broome, Mark Waid and Geoff Johns (multiple speedsters teaming up to face a crisis together.) and Green Arrow #100 (the inclusion of Veronica Dale and The Eden Corps, the plot of the hero needing to figure out how to stop an active bomb).
Granting that fanatics are not always logical, the idea of an environmental terrorist group damaging the environment by setting off a nuclear bomb to show the dangers of nuclear power doesn't make a lot of sense. The Eden Corps in the original comics acted in ways that would destroy cities without harming The Earth as a whole.
The chemistry between Violett Beane and Tom Cavanagh is as fantastic as ever. Their non-verbal acting in the final sequence as Harry and Jesse "talk" is particularly fantastic.
Grant Gustin does a fantastic job of selling Barry's exhaustion and frustration through the episode.
The effects work for depicting Flashtime is rather impressive.
The energy effects as Barry attempts to draw The Speed Force out into negating the fission engine with a fusion reaction may be the single greatest action sequence in the show's history and the history of superhero shows ever, looking just like a panel from a Flash comic come to life.
The formula the camera focuses on after the title stinger - 3x2(9yz)4A - is "The Speed Formula" in DC Comics. This was the formula said by the speedster Johnny Quick and, later, his daughter Jesse Quick, in order to use their super-speed powers.
The shoot-out between The CCPD and the Terrorists occurs at Waid Airfield. This is a tribute to Mark Waid - The Flash writer responsible for coming up with the idea of The Speed Force.
While never given an official name in the comics, the idea of "Flashtime" (i.e. speedsters being able to operate in a state of super-speed while the rest of the world around them seems to be frozen solid) has been explored in multiple comics and cartoons.
At the time this episode originally aired, there was a storyline in The Flash comic based around a similar plot, with Barry Allen, both versions of Wally West and Avery Ho (The Flash of The Justice League of China) having to work to save Central City from a device that was draining all the molecular motion from it in a bid to give Gorilla Grodd super-speed. Only Grodd, his minions in the criminal scientist cabal known as The Black Hole and the speedsters were unaffected.
The terrorist group who set off the fission engine is revealed at the end of the episode to be a group called The Eden Corps who are lead by a woman named Veronica Dale. Their goal was to show the dangers of nuclear energy.
In the classic DC Comics Universe, The Eden Corps was a radical environmentalist group whom Oliver Queen tried to infiltrate in an effort to bring them down from the inside. He would wind up sacrificing his life in order to destroy a bomb The Eden Corps was going to use that would release a virus that would eat all the plastic in Metropolis. As in the DCTVU, it was run by a woman named Veronica Dale, who went by the codename Hyrax.
The bridges between Earths formed by Cisco's powers close after three picoseconds. A picosecond is one-one-trillionth of a second. Iris says that DeVoe's teleportals may close even faster than that.
Cisco develops a complex and eloquent algorithm to track the warping signatures of DeVoe's teleporting.
Barry says that he can't run the nuclear bomb out of town as the energy involved will speed up the reaction and it would blow up before he could get out of Central City. He also says that he and Jesse Quick don't have enough time to evacuate the city and get all the people out of harm's way.
The ARGUS device that the terrorists were trying to get to is revealed to be an experimental fission engine containing deuterium isotopes. It is contained within an inertial confinement cage to stop the radiation. With enough pressure, however, the isotopes will split and produce heat and light. The light will start out blue, shift yellow and then go purple before the engine explodes.
A breach is a controlled folding of space-time. As such, when a breacher like Vibe is moving at super-speeds and in a state of Flashtime, there is a lack of sufficient time for them to open a breach.
Without a connection to The Speed Force, a body cannot withstand the stress of Flashtime for more than a few minutes. This is discovered when Cisco begins to hyperventilate after about two relative minutes examining the fission engine with Barry. Even a speedsters enhanced physiology will eventually begin to wear down after an excessive amount of time spent in Flashtime.
A person's age and physical fitness seem to be a factor in how long they can withstand Flashtime. This is why the younger and more physically fit Vibe is not effected as quickly as Harry Wells. Jay Garrick, the oldest speedster, is also the first to start showing signs of physical exhaustion the longer he, Jesse Quick and The Flash spend in Flashtime.
Space-time breaches and portals to The Speed Force operate according to different laws of physics. This means that Barry can use a Speed Force portal to dispose of the fission engine when a breach cannot be established.
In nuclear fission, enormous energy is created by a chain reaction of atoms splitting and releasing neutrons. It is nearly impossible to reverse this process, but theoretically you can restore stability through one of two methods. One is to offset the loss of mass through nuclear fusion. The other, more promising method given the situation our speedsters are in, is to cool the engine down.
The 3 million tons of energy (or 3 megatons) generated by the fission engine is equal to 3 billion joules.
A lightning bolt contains roughly 1 billion joules of energy. This leads to Jesse Quick suggesting that she, Barry and Jay each throw a lightning bolt at the fission engine in the hope that it will generate enough fusion energy to balance the equation.
The Quark Sphere is a device which is filled with Barry Allen's unique genetic marker, programmed to track his DNA using the electrical current of The Speed Force. Used in tandem with The Speed Force Bazooka, The Quark Sphere was able to trick The Speed Force into thinking Barry is still there once The Speed Force Bazooka pulled Barry out of it. Barry is able to make use of The Quark Sphere here to act as a lightning rod which lets him draw the Speed Force energy needed to send fusion energy at the fission engine.
Caitlin notes that Jay Garrick's blood glucose levels are low following his time spent in Flash Time.
Harry reworks the Cerebral Inhibitor into a device that does the opposite of its intended purpose, allowing a person to hear the thoughts of other people. Using this, he is able to convey to Jesse the emotions he cannot articulate regarding his wife's death.
Barry: Has anyone seen Ralph today?
Caitlin: No. He's downstairs moving in. He's very nervous.
Harry: I don't know why.
Cisco: I don't know why, either. He's a superhero! People with powers are ready for anything,
(Cisco turns around, nearly running into Jesse Quick.)
Cisco: Ahhhhhhh! Son of a Breach!
(Jesse looks at an odd helmet on Harry's desk.)
Jesse: What's this?
Harry: That is a mental activity dampener. It's for DA Cecile Horton. Keeps her from hearing other people's thoughts.
Jesse: It's kinda clunky.
Harry: (laughs) That's what she said. (goes serious) Literally, that's what she said. The second version's more streamlined.
Harry: I came here to stop DeVoe!
Jesse: No. You stayed because of DeVoe.
Harry: A distinction without a difference.
(Barry looks around the frozen crime scene as if searching for inspiration. His gaze finally falls on Cisco.)
Barry: I need right now you, man.
(Barry places a hand on Cisco. There is a shock of electricity as Cisco begins moving.)
Cisco: (looking around in confusion) Wha- what is going on?
Barry: You're moving with me at super-speed.
Cisco: What?! Is this what it looks like when you run?
Barry: More or less.
Cisco: (looking at the still unmoving Killer Frost) I'd say it's a little uneventful.
(Jay Garrick and Jesse Quick run in on Barry talking to the sped-up Harry Wells.)
Jay: What the heck?!
(Harry grabs at Barry.)
Harry: Get her out of here.
Barry: I'm gonna - I'll try.
Harry: (gasping) Allen... Allen.
Barry: All right.
(Harry nods as Barry lets go and Harry freezes back in place.)
Jay: How do you do that?
Barry: Uh - I'm not sure. I've been able to do it ever since I came out of The Speed Force.
Jay: That's a hell of a new trick!
Barry: Look, right now...
Jay: I know. Jesse showed me the nuke.(sighs) We're in trouble, kid.
Barry: Well, I don't know. Wells has an idea that he think might work.
Jesse: Yeah? What is it?
Barry: We send the bomb into The Speed Force. Let it detonate in there.
Jay: Like hell you will!
Barry: What do you mean? Why not?
Jay: Because, Flash, if you do that, we may lose The Speed Force forever!
Killer Frost: Barry? Don't let Caity die.
Jesse: Okay. What if... I don't know... what if we run back in time and stop this bomb from ever going off?
Barry: No. Jesse. We can't do that.
Jesse: Yeah, well, it's kind of our only option.
Barry: It's not an option.
Jesse: Even if it saves the city and everyone in it?!
Barry: It's not saving them, okay? The second you alter the timeline, everything changes. Especially the people you love. Trust me. I learned that the hard way.
Jesse: Yeah, well maybe a new version of my dad isn't the worst thing in the world.
(Barry and Iris kiss as Barry starts to let go of her.)
Iris: Come back to me.
Barry: As fast as I can.
(Joe runs over to Barry.)
(Joe puts his hand on Barry's chest as if feeling for a heart beat. Slowly, Barry's eyes flutter and he moans.)
Barry: (his voice dry and crackly) Are we dead?
Joe: ... no?
Barry: (sighs) That's good.
(Barry pants and closes his eyes, clearly exhausted.)
Barry was first shown as being able to lend his speed to other people in 410
After the opening scene, the first scene after the title stinger starts "8 Minutes, 48 Seconds Ago."
Barry is attempting to push himself to become fast enough to follow through one of The Thinker's teleportals.
Cisco is able to map every time The Thinker teleported over the past three years. These include when The Mechanic grabbed him after absorbing Izzy Bowin's powers in 414, the attack on Iron Heights Prison in 413, the alley where he abducted Barry in 409 and The DeVoes' house.
Ralph is moving into a basement room in STAR Labs, due to being nervous about being grabbed off the street by The Thinker.
Jesse Quick was last seen in 316, though a hologram of her appeared in 403.
Apology Cubes are a technology used on Earth Two, similar to Break-Up Cubes, which were first referred to in 403.
The first version of the Mental Activity Dampener from 414 is seen.
The death of Harry Wells' wife is mentioned, though the circumstances are not specified. Harry was unable to save her.
Jesse accuses Harry of never dealing with his wife's death. Harry denies this.
Jesse says that she found peace by talking about her mother's death.
Waid Airfield is one of the airports in Central City.
Cisco is unable to form breaches while operating in Flashtime. This means he cannot do what he did in 410 to send the excess radiation generated by Fallout to a dead Earth.
Jay Garrick was last seen in 323.
Jay Garrick has never seen another speedster temporarily lend their speed to a non-speedster.
Barry has been able to lend speed to other people since leaving The Speed Force.
Jay says that a nuclear explosion in the heart of The Speed Force could potentially destroy it.
Killer Frost has no frame of reference for what heat feels like until she begins to exhaust herself trying to cool the fission engine while in Flashtime.
Jay Garrick tires out before he can add his lightning to that of Barry and Jesse.
Jesse runs out of energy after trying to talk to speed up her father and, failing that, talking to him.
Iris refers to the events of 401 and how Cisco and Caitlin used The Speed Force Bazooka to extract Barry from The Speed Force.
Jay announces his intention to retire as The Flash of Earth Three as soon as he finishes training his replacement - an unnamed woman - to become the new Flash.
Barry is told to not use his powers and rest for a few days following his time in Flashtime.
The words that Jesse hears her mother saying - "Because in the vast night sky, you are the only star I see." - are the same words that the Earth One version of Tess Morgan said to Harrison Wells that inspired the name STAR Labs in 117. This seems to confirm that the Tess Morgan of Earth Two was Harry Wells' wife on Earth Two as well.
A sign on the counter at C.C. Jitters promotes a spring special on their Killer Frost iced coffee drink.
For the first time ever, Caitlin has a memory of something that Killer Frost did while in control of her body. In this case, she remembers Killer Frost being taken into Flashtime by Barry, trying to freeze the fission reactor and then Killer Frost feeling worried about her.
The mystery waiter from Barry and Iris' wedding in S308 who later made an appearance in 411 when Ralph and Cisco were getting coffee makes another appearance. This time she bumps into Harry and Caitlin, literally spilling a Killer Frost drink on their table. She makes reference to being there to meet some people for the first time and being kind of nervous - an act that fades as Harry gets annoyed and leaves while a sympathetic Caitlin says she hopes that her meeting goes well. The waiter ominiously says that "It did."
The Speed Force.
The Bottom Line
A definite improvement over the last run of episodes and a strong contender for one of the top-five best Flash episodes of all time. Rather than feeling like a piece of filler given the absence of any major plot elements from Season Four (no Ralph, no DeVoes), this episode feels like a return to basics. Even the romantic scenes between Iris and Barry don't feel as forced somehow, though that's largely down to Gustin's performance and how effectively he portrays a Barry Allen who has been working for days without sleep, from his perspective and is looking on the woman he loves as if it really will be the last time he ever sees her.