Season 2, Episode 7:
Still suffering the effects of his brutal beating at the hands of Zoom, Barry is forced back into action when Grodd kidnaps Caitlin.
At S.T.A.R. Labs, the team says Barry is almost healed and they want to help him. He still is having trouble breathing, and can barely walk. Wells comes in and asks them to help him head back to Earth-2 to try to stop Zoom. Everyone is up for it except for Caitlin.
Cisco gets an alert, but it's not urgent; it's about his date with Kendra. Barry gets a phone call from Patty and takes it; he's told her he's sick but she obviously doesn't know the details and she offers to bring him soup, which he declines. She's suspicious, but lets him go.
Caitlin goes to talk to Wells, and he's at a bar preparing to leave, scribbling notes. She tells him they can help him save Jesse, but he says he made a mistake coming to Earth-1 — that he doesn't have another plan. Caitlin tells him that the best way to save Jesse is to stay. He tells her to leave him alone, and that he needs to figure out which breach to use. Wells gets the idea that he has to close all of the breaches except the one at S.T.A.R.
Before their date can start, Cisco touches Kendra's hand and gets a vibe off of her, seeing a winged warrior. He tells her he has to go.
At a research lab, a scientist has a brief, strange vision and excuses himself. On the way out, he shatters a glass case, steals a canister and uses it to knock down another man who tries to stop him. Outside, he meets Grodd, who had been controlling him.
The next morning, Joe and Patty meet at the crime scene, where they see evidence that the scientist was killed by a metahuman. Joe excuses himself to check on Barry, saying that Barry wanted him to bring soup.
At S.T.A.R., Barry is on the treadmill, but when he starts to push himself he gets flashbacks to Zoom's attacks. He loses his balance and is thrown from the treadmill. He tells Joe that he feels like a failure because Zoom beat him in front of the whole city and now they don't have faith in the Flash.
In the S.T.A.R. breach room, Cisco tells Caitlin that he vibed on a bird-man. When he starts thinking maybe it's an angel, Caitlin gets the same vision as the scientist from before, then punches Cisco and leaves.
Patty calls Joe to tell him that first of all, the drugs stolen are used to enhance intelligence, among other things; and second that hairs found at the crime scene are gorilla hairs.
Joe comes to see Barry and Cisco, telling them that it's Grodd, just as Caitlin heads outside. They see on the security camera that she's being followed by Grodd, but neither are present when they get outside.
At S.T.A.R., Joe says he's going to look for information on gorilla sightings so they can try to track him to rescue Caitlin, who they think has been abducted. When Cisco and Wells go off to start work, Joe leaves Barry to try and figure out how they're going to subdue Grodd once they find him.
In a new lair — not his one from the sewers — Caitlin wakes up, and Grodd calls her name. She realizes that he remembers her, and he leaps down to stand near her. He says she was always kind, and that he needs help. He wants to know how he became what he is. He wants her to repeat the accident that created him so that there can be more like him. When she says she can't, he tells her to learn.
Back at S.T.A.R., a newly-motivated Barry is back on the treadmill, but turns it off when he starts to get speed lightning. His father shows up to talk some sense into him, and the two hug. In the other room, Joe congratulates Iris for bringing Henry.
After explaining Grodd's origin to Wells, Cisco asks what Wells is doing. Wells says he has an algorithm that can find Grodd — and it gets a hit. Cisco tells Barry they know where Grodd is. Barry still doesn't know how they're going to get Caitlin back, but Wells has an idea: dressed as the Reverse-Flash, they hope he can convince Grodd that he's the real deal and talk him into letting her go.
At S.T.A.R., Henry tells Barry that everyone stopped believing in him when he was convicted of his wife's murder — that he knows what it's like to have those judgmental eyes on you. Barry asks him how he got past that, and Henry says he embraced it, and that accepting it was the only way to move forward. If he could survive it and learn to believe in himself again, he could do anything. He says Barry helped him by never doubting him.
At Grodd's lair, Caitlin has a working theory on how to make more like Grodd. Before she can implement it, Wells enters and tells Grodd that he's back and they don't need Caitlin anymore. Grodd says that Wells never asked for anything, just took, and demands to know who Wells is. He throws Wells against the wall, and Barry tells Cisco, who had run to rescue Caitlin, that an overdose of the drugs Grodd stole could overload his brain and provide them cover for an escape. Wells stands up and, taking a more aggressive tone of voice, manages to fool Grodd into believing he's the Earth-1 Wells.
After delivering a monologue that sounds suspiciously like something the Earth-1 Wells would say, he sticks Grodd with a handful of needles and flees with Cisco and Caitlin.
Back at S.T.A.R., Caitlin patches up Wells. Joe suggests killing Grodd, but Caitlin objects, saying that he's lonely and sad. Wells says he has located a breach that will send Grodd to a suitable location on Earth-2, and Henry volunteers Barry to bait Grodd into the breach.
Caitlin lures Grodd out of his lair and Barry, in the Flash outfit, lures him in front of the breach. Once there, the plan is to blast Grodd to Earth-2 with a speed cannon. Barry shows up, chased by Grodd, and Cisco and Wells turn on the speed cannon. When Grodd hits Barry, he has a flashback to his beating by Zoom, but recovers when Caitlin provides cover. She tells Grodd that Flash was just trying to save her from Grodd, and isn't an enemy. She tells Grodd she can give him what he wants if he trusts her. Grodd approaches her, and Barry runs at her, dragging Caitlin away while the breach opens up and starts dragging Grodd. He resists, and Henry has to encourage Barry to kick Grodd into the speed cannon, sending the ape to Earth-2.
Back at S.T.A.R., Cisco is going to destroy the Reverse Flash suit, but Barry asks him to find out how to make it compress into the ring first. Wells says he can help, as he understand microtechnology. He tells them about the gorilla preserve where they sent Grodd, and says he's going to stay and work with Team Flash to close the breaches and rescue his daughter.
Back at home, Henry takes a number of childhood photos of Barry before he leaves town again. Joe tells Barry that Patty isn't dumb and isn't buying his story about being sick, and Barry says he'll tell Henry about the new girl on the way to the bus station. After Barry and Henry leave, Joe muses about what it would be like to have a son — something that tortures Iris a little bit since she knows he has one.
At Barry's lab, Patty confronts him about his lies about being sick. Barry says his dad was in town, and that he didn't tell her because he was convicted of murder. He apologizes for not having more faith in her, but she says it's not about Henry, it's about Barry and she needs to trust him if their relationship is going to work. They kiss.
That night after Jitters closes, Cisco brings Kendra a basket with chocolate and flowers, to apologize for bailing on their date. He tells her that there was a police emergency, and she says that working with them is very cool and brave. He's brought a digital movie projector with The Princess Bride on it so they can resume their date. Kendra reaches out to hold his hand, and he gets a much closer-up vision of Hawkgirl — now realizing it's Kendra. He reacts to it, and covers by telling her she's a great kisser. The two leave to watch the movie.
On Earth-2, Grodd is spit out into a jungle, where he sniffs and looks around. He sees a rock formation that looks like a gorilla, with a city beneath it, and roars.
- Abusive Parents: Grodd's tragic line about how father takes rather than ask pretty much tells us his relationship with Thawne was not happy.
- Absentee Actor: Jay Garrick once again.
- Antagonist Title: Not a hard guess who the episode villain is.
- Arbitrary Skepticism : Snow laughs at Cisco's idea of Bird people.
- The Atoner: Earth-2!Wells becomes this after the events of last episode. In fact, for a portion of the episode, he wants to head back to Earth-2 before "anyone else gets hurt".
- Broken Pedestal: Caitlin believes that by baiting Grodd into the breach, that he might have changed his opinion of her.
- Barry is also worried that everyone in Central City has stopped believing in him after Zoom defeated and humiliated him in front of the whole city in the previous episode.
- The Bus Came Back: Henry Allen is called in by Iris to try and help Barry regain his confidence, while Grodd is back trying to make more Grodds.
- Career-Ending Injury: If not for Barry's healing abilities, Zoom breaking his spine in the previous episode almost certainly would have been this.
- Chekhov's Skill: The fact that Henry was a medical doctor gives him the confidence to trust that Barry had physically healed and that what was really holding him back was psychological.
- Cliffhanger Cop Out: Subverted. The Stinger from last episode made a big deal over how Barry was paralyzed. Good news? Barry still has speedy healing, so he's up and walking again pretty fast. Bad news? Barry's depressed over Zoom kicking his ass, and isn't 100% back to normal yet...
- Especially funny since, after the "Previously On" recap, the literal first scene is of Barry walking with a cane.
- Curb-Stomp Battle: Barry is still recovering from the one Zoom dished out. He suffers another one at Grodd's hands, although it's far less brutal.
- Daylight Horror: Caitlin socks Cisco, and Joe tells the team that Grodd is back. Team Flash skims through STAR Labs' security cameras, trying to find her, and suddenly see Grodd walking into the shot just as she exits the building.
- Dramatic Irony: When Joe is musing about theoretically having his own (biological) son, Iris looks distraught, because she and the audience know he most likely does.
- Dungeon Bypass: Flash plays cat and mouse with Grodd throughout the city streets, to lure him into a breach. The ape manages to catch up in short order courtesy of his patented "King Kong" Climb.
- The Dreaded: With Grodd on the loose again, all those in STAR Labs are in full alarm.
- Emergency Impersonation: Tonight, as part of a plan to deal with Grodd, the role of Reverse-Flash will be played by Earth-2 Wells. Barry does not take this well.
- Eureka Moment: After Caitlin (upset that she didn't convince Earth-2!Wells to stay) remarks that it's a good thing Cisco and Professor Stein never figured out how to close the breaches (because he'd be stuck here otherwise), Earth-2!Wells comes up with a plan: close all of them except the one at S.T.A.R. Labs, leaving Zoom with one exit.
- Even Evil Has Loved Ones: As before, Grodd has a big soft spot for Caitlin, and he's more than a little pissed when he realises that Earth-2 Wells is posing as "Father".
- Cisco twice gets a vibe off Kendra that reveals her appearance in costume as Hawkgirl in Legends of Tomorrow.
- Wells mentions how his Earth also has super-intelligent apes, which initially could be seen as a Mythology Gag to Monsieur Mallah or Gorilla Boss. However, at the end of the episode, Grodd is dispatched by sending him to Gorilla City on Earth-2.
- The Fourth Wall Will Not Protect You: Wait, why are the viewers seeing visions of Grodd's Dark and Troubled Past every time he has someone under his mind control?
- Good Thing You Can Heal: If Barry didn't have his accelerated healing factor, he would pretty much stay in a wheelchair for the rest of his life.
- Hes Back: As pointed out by Cisco after Barry knocks Grodd into the breech:Cisco: Welcome back, Flash.
- Imposter Forgot One Detail: Grodd identifies Wells as an impostor because "his" Wells never asked permission to take something.
- Internal Reveal: Cisco explains Grodd's backstory to Wells.
- Leaning on the Fourth Wall:
- At the start of the episode, it was mentioned that a week passed since Barry's spine broke.
- Near the end of the episode, Barry gleefully tells his father that he'll take him to the bus station, hilariously acknowledging the fact that Henry was about to be literally Put on a Bus again.
- Locked Out of the Loop: Henry is understandably confused when the supposedly dead Harrison Wells shows up in STAR Labs. Barry introducing him as the Harrison Wells of Earth-2 doesn't exactly help, although Henry takes it all in his stride.
- Megaton Punch: Grodd's last victim (before Team Flash discover he's at large again) was killed this way. Joe's mouth was agape when Patty pointed out the point of impact a story high.
- Muggles Do It Better: Cisco designs special devices that can block Grodd's telepathy.
- Mythology Gag:
- The place on Earth-2 where experimental gorillas are freed and allowed to roam? Gorilla City.
- Atlantis is visible on Wells' world map of Earth-2, and one of the breaches leads there.
- Barry asks Cisco to work out a way to keep his Flash costume in a ring the way that Reverse-Flash did with his. In the comics, this is the Flash's trademark method of carrying his costume.
- While mistaking his Vibe of Hawkgirl as a man, Cisco thinks it could be an angel. Zauriel was an actual angel who joined the Justice League in the late '90s as an Expy for Hawkman, who was Exiled from Continuity for his massive Continuity Snarl at the time.
- Nerves of Steel: Wells holds up pretty well against Grodd; despite Grodd working out that he isn't "Father" and attacking him, Wells doesn't panic and keeps up the act, distracting Grodd long enough to subdue him and escape.
- Oh, Crap!: Joe's reaction once he realizes who is responsible for the recent series of thefts and murders.
- O.O.C. Is Serious Business:
- Joe has often shown up at STAR Labs with urgent information. He's never previously burst in running and yelling in panic.
- Barry is normally laid back and friendly. When he sees Wells in the Reverse-Flash costume, he finally uses his powers since his fight with Zoom, pins him to the wall, absolutely enraged before realising who's actually in the suit.
- Plot Armor: When Grodd hits the scientist at the beggining of the episode, the scientist died. When he did the same to Harry, he's just injured.
- Then again Grodd may have held back (very possibly, since Harry didn't fly as much as the murdered scientist), or the fact the futuristic material of the costume saved Harry.
- Pun-Based Title: The title is taken from the term Guerilla warfare. But since Grodd is the episode's villain...
- Put on a Bus: Henry again at the end of the episode. Lampshaded by Barry.
- Scary Animal Title: The word scary describing Grodd is an understatement.
- Seen It All: Wells isn't surprised by there being an intelligent, talking gorilla, he's just mildly interested that Earth-1 has them as well. Also doubles as Foreshadowing how Grodd is dealt with.
- Ship Tease: Between Caitlin and both Harry and Grodd, Kendra and Cisco, and Barry and Patty.
- Shirtless Scene: Harry gets a downplayed version, wearing a black tank top that he pulls up to expose his abs while Caitlin stitches up his side after his encounter with Grodd. It turns out that the guy is remarkably fit for a scientist.
- Single-Episode Handicap: Not even. Barry's legs work pretty much fine before the halfway point of the episode.
- Take a Third Option: With no clear idea on how to prevent Grodd from continuing his plan other than killing him, Wells suggest an alternative: use a breach to send him to Earth-2 and a place where he can find others like him.
- Terminology Title: Pun-Based Title aside, the episode title is derived from the term Guerilla warfare, which means a small group of combatants such as paramilitary personnel, armed civilians or irregulars (The S.T.A.R. Labs crew) use military tactics including ambushes, sabotage, raids, petty warfare, hit-and-run tactics, and mobility to fight a larger and less-mobile traditional military (all of which the main characters tried throughout the episode).
- Throwing Off the Disability: Barry fully recovers the use of his legs for standing, walking, and even Super Speed over the course of the episode. Justified due to his speedy healing.
- Took a Level in Kindness: Wells finally starts to warm up to the team and the feeling is reciprocated when Wells risks his life to save Caitlin from Grodd.
- Tragic Monster: Grodd gains aspects of this, which Caitlin empathizes with; he's growing more intelligent, but he's also growing lonely because there's no one he can relate to.
- You're Not My Father: Said word-per-word by Grodd towards Harry.
- Woman in White: Caitlin spends the entire episode dressed in all white.