While the Turtles are infiltrating an undersea Kraang base, the Foot Clan attempts to capture April.
This episode provides examples of:
- Book Dumb: April mentions she's failing trigonometry.
- Damsel in Distress: The Foot Clan is after April this time but she takes care of it.
- Call Back: Murakami returns after being absent since "I, Monster".
- Cool Bike: Karai owns a sleek red-and-black motorcycle. It appeared for a brief moment in the previous episode, but gets a lot more screen time here. It bares more than a passing resemblance to a Kawasaki Ninja.
- Curb-Stomp Battle: She managed to land one lucky hit and take advantage of a momentary distraction to win at the end, but April was no match for Karai.
- Did I Say That Out Loud: After the turtles have gotten back to the Lair and Donnie is frantically trying to contact April on his T-Phone.
Donnie: Come on, April! Come on, April!
April: Hey Donnie!
April! You're okay! You hear that, guys? My sweet princess is alive! [Beat]
Did I mute that?
April: Let's agree that you did.
- Foreshadowing: April is unharmed by the pure Kraang-water that a moment before had completely dissolved a pizza slice.
- Freeze-Frame Bonus:
- Donatello's caller ID on April's phone is labelled "Donny Boy", and his picture is decorated with a bow on his head and with flowers and stars around the border.
- A quick eye will notice Karai's order at Murakami's restaurant before she says what it is: The wooden piece has a Turtle on it.
- Getting Crap Past the Radar: Not only does the sea monster mount the Turtle sub, but Mikey quips "We're not that kind of sub!" The guys' faces as they realize just what the monster is doing arguably makes this a Crowning Moment of Funny.
- Green-Eyed Monster: Karai demands to know what makes April so special while she's pounding her into the dirt.
- Hamster Wheel Power: The Turtle Sub is equipped with jets for quick action, but to charge them up and for stealth it also runs on three bicycles that move the flippers. Leo, Raph, and Mikey are the power source for those.
- Heroic Bystander: Murakami dumps a bowl of soup on Karai and stalls her to help April escape, all while pretending to be a blind klutz.
- Heroic Resolve: No matter how many times Karai beats her senseless or throws her down, April just keeps getting right back up try again.
- Innocently Insensitive: Donnie's reaction to April having to give up her entire life. (At least temporarily)
- Jerkass Has a Point:
- When April calls the turtles for help against Karai, Don wants to abort the mission and help her, but Raph points out that foiling the Kraang's water poisoning plans are more important otherwise they'll be endangering everyone in New York including April.
- In Space Heroes, the Captain states that if they keep bailing out their trainees, they'll never learn how to take care of themselves. This falls under Sink or Swim Mentor given the circumstances of those trainess.
- Made of Iron: The Kraang creature survives the explosion of the base with no ill effects.
- Meaningful Name: Karai goes under the fake name Harmony when pretending to befriend April. The name Miwa can mean Harmony.
- Missing Mom: Mentioned by April and it's implied Karai may also fit this trope.
- Mythology Gag: The turtles' masks all look red through the sub's windows.
- Never Say "Die": Averted as the Sea Monster "attacks" the T-Sub:
Donnie: "That's it! It's got us! WE'RE GONNA DIE!!"
- Never Trust a Title: Despite the name of the ep it doesn't have a vendetta. Karai yes, Vendetta no.
- No-Holds-Barred Beatdown: A mild version, but Karai lays into April when the two finally fight.
- Not So Different: April and Karai are both ninja with father issues.
- Oh, Crap: April when she realizes "Harmony" is really Karai.
- Pet the Dog: Karai genuinely feels sad for April when she learns she has a Missing Mom.
- Reality Ensues: In addition to April's training as a kunoichi averting Instant Expert, her fight with Karai makes no attempt to dodge the hard truth that someone who's been training for years and has been in actual fights is going to beat someone who has never been in a serious fight and has only been training for, at most, a few months.
- Staircase Tumble: Karai doesn't so much fall down the subway stairs as get bodily thrown down them by April.
- Stock Ness Monster: The Kraang sea creature guarding the base bears a great resemblance to many illustrations of Nessie and plesiosaurs in general.
- Storming the Castle: The tradition of the Turtles sneaking into Kraang labs continues.
- Tempting Fate: While in the Kraang's underwater lab, Leo tells the others to be quiet. Don points out there's no need for Leo to say that everytime since they're ninjas and they know how to be quiet. Cue Don's T-Phone ringing.
- Underwater Base: The Kraang's base in this episode.
- You Can't Go Home Again: With both the Kraang and the Shredder out to capture her, Splinter and the Turtles decide that April will have to stay in the sewers with them for her own safety, at least until the crisis is resolved.