Larry was talking with Ludwig and Wendy in the lounge.
Larry: So do you guys think we've seen the last of the crystal keepers?
Ludwig: Unlikly. It's been just two days, and there was a week between Bonnie and Drystone.
Wendy: If I ever get my claws on that creep! He'll be sorry he exists!
As usual, Kamek knew exactly what they were saying. He had changed Roy back to normal. But Roy was not the keeper either, and Morton was still in the hospital from Bonnie's sabotage. It was Kamek’s job to make sure the Koopalings didn't find out too much. He watched intently on his crystal ball until he heard a noise and whirled around to see Popple.
Kamek: You're losing your touch, Popple.
Popple: You heard me ‘cause I let you, see. Drystone insists that Jr. knows too much about him, see.
Kamek: Very well, I suppose I should deal with Ludwig then.
Popple: That's right. I'll throw this castle into chaos and nobody will notice while you work, see.
Kamek: You'd better get started then, they know who you are, Popple.
Popple: Not a problem, see.
And with that, he left to find Jr.
Kamek: We'll know if it's Ludwig or Jr. by tonight.
Kamek began preparing his invisibility potion as Popple went to work. He went straight through the walls. That was one of his two powers; each of the keepers had two. Bonnie and Drystone had each shown off only one of their tricks: energy spheres and magic respectively. Popple saw Iggy walking by from inside the wall and pulled him in.
Iggy: What the-
Popple had already thrown the old mask on Iggy the mask he'd used to turn Bowser into Rookie. That was his second ability; until someone new donned the mask Iggy would be his. He pulled the blue mask off and sent Iggy on his way.
Iggy walked straight down to Ludwig's lab, knowing his older brother wasn't there. Iggy quickly took a can of knockout gas and hid it under Ludwig's pillow, set to go off after dark. He left and walked straight into Roy.
Roy: Watch it, Four-Eyes. What were you doin’ in Ludwig's room? Better tell, or else.
Roy made a fist but Iggy smiled. Roy lunged but Iggy, now with Popple controlling his movements, ducked and slammed Roy into a wall. Roy turned, but Iggy had his wand out and enlarged Roy until he hit his head on the ceiling, then Iggy shrunk him and squashed him like a bug while he was stunned. Iggy grew him back and left Roy's unconscious body behind.
Popple was proud of his work. Knowing his plans would succeed, he smiled and sent Iggy after Jr.
Elsewhere, Larry was listening to his spy-radio. It picked up noises around the castle. He then heard what sounded like demented laughter and Jr. screaming.
Larry: What in the world? I'd better check this out.
He ran down the stairs and around the corner to Jr's room. Wendy and Lemmy had beaten him there. He saw that his brother’s room was a wreck and that Jr. was gone.
Larry: What happened?
Lemmy: We don't know. We heard Jr. scream and came to find this.
Wendy: This has keeper written all over it. Larry, go tell Ludwig.
Larry: We'll need him, see ya.
Larry ran down the halls toward the lab. He was scared. That laugh had sounded just like Iggy. He didn't want to say that Iggy had something to do with it, especially with Lemmy around. He got to the lab, but no one was there.
Larry: I'll wait here, Ludwig will show up.
Ludwig was actually in the halls himself, headed for his lab, when suddenly someone threw something over his head and he blacked out. Popple smiled as he came out of the wall.
Popple: With Iggy and Jr. tied up, this'll be a snap, see.
Popple pulled the mask off Ludwig and watched as he walked off towards his lab. When he got there, Larry ran straight up to him.
Larry: Ludwig! Something happened to- ACK!
Ludwig had blasted him with his wand, as he then walked over to his bed. He pulled the sleeping gas from under the pillow and inhaled as much as he could before passing out. Kamek came into the room completely invisible and saw the two of them.
Kamek: Ludwig first, then Larry.
He went to work with Ludwig.
Elsewhere, Popple was slinking through the castle looking for a victim. Not just any victim, but Bowser himself! He came upon Bowser's room and walked in.
Bowser: Popple! What are you doing here?!
Popple: Wondering if you could give me a hand with my biggest heist yet, see.
Bowser: Fine. Where is it?
Popple: You should wear your old mask first, we have to leave now, see.
Bowser puts on the mask but stops moving afterwards.
Popple: It's your treasury, see.
Meanwhile, Wendy and Roy were walking down the hall to Ludwig's lab to see if Larry had found him. As they approached, Kamek just discovered that Ludwig was not the keeper and was about to check Larry.
Kamek: Argh. Someone's coming, at least I'm still invisible.
He walked out of the room, right past Wendy and Roy. They then saw Larry and Ludwig, and woke them up.
Wendy: What happened to you two?
Ludwig: Someone threw something over my head and I don't know what happened next.
Larry: You knocked me out. And what's that can by your tail?
Ludwig: Knockout gas. I must have gassed myself!
Wendy: Then there's another keeper here! He must have some kind of mind-control.
Roy: Then let's get him!
Larry: Guys, when Jr. disappeared, I heard Iggy laughing. I think the keeper has him too.
Ludwig: This is bad, what if he is still controlling one of us?
Roy: Is he, Kooky?
Ludwig: Do. Not. Call. Me. That.
Roy: He's real.
Wendy: It's a risk we have to take. Come on, we have to find this creep.
As she said this, an alarm went off.
Larry: I thought I disabled the treasury's alarm?
Wendy/Roy/Ludwig: You did what?
Larry: Nothing! Let's go!
They ran down and saw Popple and "Rookie" robbing the treasury.
Larry: King Dad?! Popple?!
Popple: Oh great. I don't have time for you brats, see. Rookie! Get them!
Bowser charged at his kids, but they all dodged. Ludwig flung a can of sleeping gas at him and he fell over.
Ludwig: Thanks for the idea! You're one of them, aren't you, Popple?
Popple: What if I am? You'll never catch me, see.
They all dived at him, but he phased through a wall and ran off.
Roy: That lousy, little-
Larry: No time, he's responsible for Iggy and Jr.
Popple was already headed for the two tied-up Koopas, when he came to an unwelcome sight: Iggy, Lemmy, and Jr, with very angry looks on their faces!
Lemmy: Got you now, Popple!
Iggy: You're gonna pay!
Jr: What they said!
Popple started to run, but Jr. threw paint on the ground and he slipped and fell. Iggy shrunk him and Lemmy rode over him while he was down. But Iggy's spell wore off and Popple got back up. Popple then pulled out his sack of tricks and yanked out a smart bomb! He threw it and the whole room came down.
Popple: Ow, see. Nobody beats Popple, see.
Jr. crawled out of the rubble and Popple threw the mask over him.
Popple: You're coming with me, see.
Jr: Yes Popple!
The two ran off as Bowser, Ludwig, Roy, Wendy, and Larry reached the unconscious twins.
Larry: They have to get to the hospital! Wendy, Ludwig, help me out.
The three carried them off as Roy and Bowser shifted through the debris.
Bowser: Jr. isn’t here! POPPLE!!!
Later in the crystal keeper's headquarters, Popple received many congratulations.
Bonnie: Nice job, Kamek crossed Ludwig off the list and now we have Jr. too!
Drystone: Not bad, Beanie.
Popple: Stop calling me that, see!
Swaps: Oh boy oh boy oh boy I really hope that it's him and that our search is over and that we can celebrate with world domination and lots of coffee and that I didn't drink it all this morning!
Bonnie: We need to keep him away from the fridge.
Paradox walked over to his fellow keepers, his gloved hands on the black, diamond-handled cane with which he always walked. He had bad news for his partners. But also some good news.
Paradox: Calm down, Swaps, I can sense that it isn't him.
Other keepers: Dang it!
Paradox: Don't worry though. Our search ends now. With only three Koopas left, it's my turn to meet them.
Drystone: What? You can't go in that castle. I like the world when it still exists, thank you.
Paradox: Nothing that drastic, Drystone; but once all three are outside its walls, I shall discern the true identity of the keeper for myself.