Underwater on Piscciss, a Magister Plumber named Pyke is searching for something. He finds a swimming object, which happens to be Ultimate Aggregor, who seems to defeat Magister Pyke.
Meanwhile on Earth, Ben is surrounded by fans and transforms into Goop in order to escape but fails, requiring Gwen and Kevin to save him. Ben receives a message from Pyke about Ultimate Aggregor on his Ultimatrix, and Ben's team goes to planet Piscciss in the Rust Bucket 3 to search for Pyke, but they are attacked by a squid-like monster. They use the electrical gauntlets in their Plumber suits (specially modified by Kevin) to defeat the monster, but in the battle, Kevin's helmet cracks.
With Kevin drowning, Gwen blasts him against the jet's side, causing him to absorb the jet's coating, saving him from being crushed by the water pressure. A nearby fish appears and is able to convert itself into a helmet for him so he can breathe. Pyke shows up and they go with him to find Ultimate Aggregor. Ben's helmet cracks when they battle some sea creatures and he transforms Humungousaur (who cannot breath underwater). He scares them off and transforms into Ampfibian instead.
They pass the guards once they explain their Plumber business, and go to the core of the planet, where it looks like Ultimate Aggregor is attacking. The core has air in it, allowing them to operate without their suits, while Pyke uses a water helmet to breathe. But a tremor occurs and Pyke is crushed by a rock. While Gwen stays to help him, Ben and Kevin go on, but find Ultimate Aggregor grabbing the planet's core piece that keeps it together.
It turns out the anti-gravity multiplier that holds Piscciss together is the second piece of the Map of Infinity, which Professor Paradox disguised so no one would not suspect it. Ultimate Aggregor leaves and Ben transforms into Big Chill and chases him, leaving Gwen, Kevin, and Pyke with the core guards. Big Chill transforms into Ultimate Big Chill when the guards keep distracting him, and Pyke accuses Ben and his friends as the culprits for stealing the core piece. Ultimate Aggregor takes advantage and escapes Piscciss in all of the commotion.
Ultimate Big Chill transforms into Goop again, and tries to stop Piscciss from shattering into pieces by using his Anti-Gravity Projector as a substitute, but it also sucks in Goop. Soon, the water turns green and Piscciss pulls itself back together, with Goop transforming back to Ben and being saved before he drowns.
Pyke thanks them for their help and Kevin wards off the fish that was used as his breathing helmet, much to his sadness, while Gwen consoles him.
Aggregor obtains the second fragment of the Map of Infinity.
Ben re-unlocks Ripjaws by scanning some Piscciss Volann (off-screen).[DM 1]
Ben: Guys, I need backup, stat! Help me, I'm surrounded! I'm serious, they're everywhere please! (girls scream) Not the Ten! NOT THE TEN!
Ben: (after getting rescued from a mob of screaming fans) Not... one... word. Kevin: S'okay, I took pictures. (shows his phone)
Ben: (Talking into radio) This is Rust Bucket 3, requesting permission to land... d-dive, over. Kevin: Maybe their communications are out again. Gwen: It could be Aggregor. I'm definitely sensing him on this planet... somewhere. Ben: No point waiting around for an invitation; take us down.
Kevin: Guys? (his Plumber helmet starts cracking) Ben and Gwen: KEVIN! (Kevin's helmet bursts open, and Gwen sends Kevin flying over to the Rustbucket, causing him to absorb the metal on the ship) Ben: Good work, Gwen. Another second and he'd have been crushed by the pressure down here. (Kevin is wriggling around and points at his neck, making it obvious that he is still unable to breathe) Gwen: But he still can't breathe! (A fish swims over and puts itself over Kevin's head. Ben is about to go over and get the fish off) Gwen: No, wait! (The fish turns into a helmet, meaning that Kevin can now breathe, so he gasps for air) That thing just saved his life! Kevin: Yeah, but I look like a dork! Gwen: What's it like? Kevin: The air is cold, but okay, and it smells a little... Ben: Fishy? Kevin: (sarcastically) How'd you guess? Pyke: Next time you decide to crash into my planet, give me some warning or would that cause unnecessary panic. Kevin: Pyke? Pyke: Got your distress call. Gwen: Just the guy I wanted to see. I can scan you to find Aggregor. Pyke: Be my guest, but you're wasting your time. Our scanners aren't picking him up anywhere in the entire planetary ocean. Gwen: (puts her hand on Pyke's head to track Aggregor) That's because he's not in the water. He's inside the planet's solid core. Pyke: The core is the most inaccessible place in the world. There's only one way in, and it's under constant guard. Kevin: (referring to Gwen) Trust me, fish lips, she's never wrong. Pyke: (the fish-helmet on Kevin's head purrs) Nice hat.
Gwen: (makes large shield around Ben and Kevin for the natives) Kevin: What'd you do that for? Gwen: Thought I'd let the local authority handle things. Ben: How come I was never that cool as Ripjaws? Kevin: You were never that cool, period.
Aggregor: Clever of Paradox to disguise this piece of the Map of Infinity as the single most important item on this planet. (Ben reaches for the Ultimatrix) Don't even think about it. If you move, I'll destroy it. And planet Piscciss... Kevin: Comes apart at the seams. The tremors before? That was you trying to get it loose. Aggregor: You're smarter than you look, boy. Admittedly, not a great achievement...
Aggregor: Next time, try absorbing something that doesn't conduct electricity! (jumps through ceiling) Kevin: You're not getting away that... AGGREGOOOORR! Ben: You completely forgot about me, didn't you? (in a muffled voice from under the rocks)