At K-Ghoul, Cassidy is doing a broadcast.
Cassidy: That's why I'm here to tell you the truth. There aren't any real ghosts in Crystal Cove. It's like the open-all-hours gym-it just isn't open all hours. And that's just the tip of the false-berg. Give me time, and I will tell you everything I know about Crystal Cove enough to blow your mind.
The wall beside her is blown open as a robot that is made to look like a Nazi World War II soldier came in.
Cassidy: You just made a big mistake.
Cassidy throws DVDs at it, but it does nothing as it attacks but Cassidy avoids it. Cassidy tries to attack it with a microphone stand but fails as Kriegstaffebot throws a chair at a window breaking it. Cassidy then kicks it head off.
Cassidy: Don't think you can come in my house and make a mess.
The eyes on the robot begin to beep as it prepares to explode.
Cassidy: Oh, great.
Cassidy gets out as the entire building is destroyed in the explosion.
Sheriff Stone along with firefighters and Mayor Nettles as he questions Cassidy.
Cassidy: You know what caused the explosion?
Cassidy: Faulty wiring.
Sheriff Stone: Works for me. Wrap it up, boys. We're heading out.
Mayor Nettles: That's it? Faulty wiring? You're not even going to investigate?
Sheriff Stone: Faulty wiring is a win-win-win situation. Minimal paperwork for me, insurance money for the station, and a new public pool for the town.
Mayor Nettles: A public pool? What do you mean?
A destroyed pipeline was leaking with water and the water filled the hole.
Mayor Nettles: Case closed. Van Ghoul movie at my house?
Sheriff Stone: I'll get my smoker.
They drive off as the gang arrives.
Daphne: Cassidy! We heard about the explosion. Are you hurt?
Fred: We brought ointment.
Cassidy turns around with a shotgun.
Shaggy: She hates ointment!
Cassidy: Hit the dirt!
The gang all get down as a Kriegstaffebot tries to attack but is shot down.
Daphne: Cassidy, what's going on?
Velma: Start with why there's a World War II-era robot on the ground.
Cassidy: We can't talk here.
At the Clam Cabin, Shaggy and Scooby get food and go back to the others.
Shaggy: Like, dude, why were you attacked by a robot?
Cassidy: Actually, I've been attacked by six robots. It started last week, and it's getting worse. I would have told you sooner, but you all don't trust me.
Y/N: For good reasons too. You lied to our faces.
Cassidy: I hear you. But I've changed. Ask me anything, and I will tell you the truth.
Daphne: Okay. What's the story with you and Mr. E? Why did you help him?
Cassidy: It's, um, complicated.
Daphne: Wrong answer.
A Kriegstaffebot emerges from the water.
Velma: Hold on, gang. Check this out.
Velma pulls out a snail.
Velma: Interesting. This is a Lassiter Gringol mollusk.
Scooby: Looks like a snail. Yecch!
Velma: It is a snail, Scooby, a rare sea snail whose picky mollusk diet restricts it to a deep Costa marine trench, located right off Crystal Cove. These robots must have an underwater origin in that trench.
The Kriegstaffebot then attacks the group but is shot in the chest by a harpoon by Skipper Shelton.
Skipper: Go back to the deep where you came from, you scurvy tin fish! You rusty scalawags are worse than sea lions! Sorry about that, kids. Free brine and cuttlefish on the house.
Fred: Gang, we need to get to that trench.
Daphne: And I know someone who can get us there.
They all wait by the coast as Tom and Tub, and their seal come out from the water.
Daphne: Everyone, this is Tom and Tub.
Tom: Sorry we're late. Tub couldn't fit into his wet suit.
Tub: It's not me! It's the suit!
Shaggy: Like, little dudes, why are you talking so loud?
Tom: Loud? Oh, our ears are probably clogged.
Tub: Sorry. We spend so much time in the water, we forgot about that. Hang on!
They hit the helmets and looked at Shaggy.
Tom: There! Is that better?
Scooby: Uh... No.
Tub: Yay! It worked!
Daphne: Thanks, guys. This is a big favor, especially since it's past your bedtime.
Tom: Are you kidding? We'd do anything for our favorite babysitter except give up pie. Right, Tub?
Tub: Aw, lay off! Pie's delicious.
The seal walks up to Shaggy and Scooby scaring them.
Tom: Aw, Scooby won't hurt you. Will you, Scooby?
Shaggy: Like, you hear that, Scoob? Looks like you're not the only Scoob!
Scooby: Scooby-Dooby, too?
The seal eats Scooby's snack bag.
Shaggy: Technically, that was Scooby's doggie bag, so, like, it's as much his as yours.
Velma: Those are your deep sea diving experts, Daphne?
Cassidy: Some weird kids you baby-sit.
Daphne: Those weird kids are the sons of Dr. Paul Williams and captain Michael Murphy.
Velma: The Simon and Garfunkel of marine biology? No way!
Fred: So, are you guys sure that you can get us all the way down to that trench?
Tom: No problem! That's where the undersea town is.
Fred: Wait. Hold the phone! There's an undersea town?
Tub: Sure! We used to go all the time until those German robots ruined it. Dumb ol' robots.
Y/N: Yeah, it was part of Crystal Cove until it sank into the water.
Velma: But how are we going to get there?
Tom: We'll take Moby!
They submarine Moby emerges what looks like a whale.
Tom: Relax. It's just Moby-dick, our sub.
They all put on diver suits and air tanks.
Tom: Get to know your air tank. If Moby loses power, and we have to bail, you can't breathe water. Trust me, we've tried.
Shaggy: Like, isn't it too dark to dive? How can we see anything if we can't see anything?
A green glow then appears.
Shaggy: Oh. OK. Like, that's better.
Scooby: Sh-Sh-Shaggy.
Shaggy turns and sees the ghostly head of Abigail.
Abigail: Go no further! There is nothing for you beneath the waves except doom! Travel below those waters, and you shall never see your home again.
She then fades.
Scooby: Well, the ocean's a dead end.
Shaggy: Yeah! Like, dry land it is.
Fred: Are you kidding? That weird ghost head just rolled out the welcome mat. We're going to need all the air we can carry.
Fred gives the two a handful of air tanks as they drop them and enter the submarine and Shaggy and Scooby look out the window.
Shaggy: Like, did you see that, Scoob?
Scooby; Yeah! Close one!
Shaggy: Um, I was talking to Scooby.
Scooby: I'm Scooby.
Shaggy: No, he's Scooby.
The seal barks.
Scooby: But then who am I?
Shaggy: Like, you're Scooby, too. You're just, uh, old Scooby.
Scooby: What? Old? I am not old!
Y/N was sitting alone as he stared at his disc piece. Cassidy walks over to Daphne.
Cassidy: I always thought you two made a great couple.
Daphne: Thanks.
Cassidy: Let me tell you something. The heart wants what the heart wants. Don't remember that too late. You'll regret it.
Daphne: What are you trying to say, Cassidy?
An alarm sounds.
Fred: What is that?
Tom: We're just entering the midnight zone.
Tub: That's where we're so deep, we're in total darkness. Here, watch this.
They turned off the lights ahead and it was total darkness.
Shaggy: Hey, where'd everything go?
Tub: Oh, it's still out there. We just can't see it. Pretty neat, huh?
Fred: Okay, but we don't want to crash, so we better turn the lights back on.
Tom: Hands off, dude.
Tub: No one touches the buttons but us.
Fred: Fine. But-
Tom: No buts! Our sub! Are we clear?
Fred: Listen, you little-
Y/N: Okay, that's enough. Tom, Tub, don't make me get Daphne over here. But for now, knowing Daphne, she'll put you in time out.
Fred: Yeah, you too need a-
Y/N: That's a time-out for you, too, Fred. Lights on, tub.
Tub turned on the light and a giant squid was in front of them.
Gang: Giant squid!
Tom: Ah, no big deal.
He presses a button, and it shocks the squid, and it swims off and they see the underwater town.
Tub: There it is, the undersea town!
Y/N: This is it. The town that sank underwater three hundred years ago.
Velma: When did you guys find this?
Tom: I don't know. A while ago? Never ran into any missionaries, though. Just robots.
Tub: Dumb ol' German robots.
Velma: Some say the missionaries' disappearance was the beginning of the curse of Crystal Cove.
Shaggy: Like, robots and curses? Ho-ho! No thanks!
Scooby: Which button takes us home?
Fred: Forget it, guys. My mystery sense is totally tingling. We got to take a closer look at that town right now.
The submarine lands on the ground as they all swim out and see multiple holes.
Daphne: Jeepers, Y/N. Look at all those holes.
Y/N: It looks like somebody's been digging.
They then find the skeletons of the missionaries.
Daphne: I think we just found out where the missionaries went.
Velma: Yeah, out for seafood.
Shaggy: Like, ho-oh! It's a shame they finished dinner.
Daphne: Shaggy, the food would be three hundred years old.
Scooby: Mmm! Let's check the cupboards.
Y/N slaps himself as he joins Shaggy in opening the cupboards.
Shaggy: Pickled eggs! Pickled ham hocks!
Y/N opens a cupboard and sees a Kriegstaufenbot.
Y/N: A Kriegstaufenbot.
Y/N closes the cupboard and pauses as he opens it again.
Y/N: A Kriegstaufenbot!!!
Cassidy: Swim!
They all swim out as three more Kriegstaufenbots destroy the building and chase the gang.
Fred: We can't out-swim them. They're too fast!
Daphne: Tom, tub, we need help!
The Kriegstaufenbots takes Shaggy's. Velma's, and Y/N's helmet as they hold their breaths. The submarine lands destroy the robots as the mouth opens and they all go up for air as three more robots begin to slam the submarine to the ground.
Tom: Hang on! Moby's going down!
Moby crashes as the water overtakes the gang while Cassidy pulls a lever, and the airlock doors open and empties the water.
Tom: Huh?
They then fall off a cliff as water begins to leak in.
Tom: Moby's messed up and venting oxygen!
Tub: We need a place to lie low and make repairs!
Shaggy: Like, how about that place?
They see an underwater base and they enter the base as the gang comes out onto a platform.
Fred: How fast can you fix Moby?
The ghost of Abaigail appears.
Abigail: You did not heed my warning. Now, the sea will make you pay with your lives.
The ghost vanishes as a door closes below them and above them and water begins to fill the room, and everyone begins to float in the water.
Daphne: Fred, this is a trap.
Fred: I know. A really good one, too. I think I'm tingling again.
Y/N slaps him.
Y/N: No tingling! Focus, Fred! What do we do?
Fred: Oh, right. Uh, let's see. Looks like an early version of the Heinrich Aquabox, so A release valve should be right...
He goes underwater as the water rises and overtakes the gang. The water then drains as Fred smiles.
Fred: Fred one, trap zero.
The door opens as they all sneak around.
Cassidy: Let's move before Uberhead shows up again.
Daphne: Tom? Tub? Are you going to be okay here alone?
Tom: Sure! Our dads once left us alone on a reef for two weeks!
Tub: We sucked on sea urchins for nourishment. We've got ocean skills!
Y/N and Daphne join the others as they see robots mining.
Shaggy: Like, it looks like those robots are mining for something.
Fred: Quiet, Shaggy. They'll-
A Kriegstaufenbot walks over as lifts the mine cart and sees nothing. The gang enters a vent and begins to crawl as they hear music and opens the vent and sees more robots being built.
Fred: Well, I guess we know where Kriegstaufenbots come from now.
The ghostly figure of Abigail appears.
Abigail: So, you still live. Well, I promise you, the sea is more forgiving than my robots.
The mechanical arms destroy the vents as the gang is sent to the ground and the unfinished robots begin to rise. They all begin to run as Shaggy trips as more and more robots awaken.
Shaggy: Like, those parts want to turn us into parts! Aah!
More whole robots are built.
Fred: Forget about the parts. I'm worried about the whole robots. Come on!
They all run into another room and the robots walk past them. They turn and see they were in a baby's room filled with baby robots.
Velma: What the...
Cassidy: You said it, sister.
Y/N: This is not creepy at all.
Fred: Go. Baby robots are still robots.
Scooby picks up a baby robot.
Scooby: Right. They're just cuter. What?
The baby robot wakes up and roars at them as more baby robots begin to cry. Y/N takes the baby robots and dropkicks him away as the Kriegstaufenbots enter the room. The ghostly figure of Abigail appears.
Abigail: There is no escape!
They all run down the hallway as Cassidy sees the main control room.
Cassidy: Look! The control room! I bet the head zeppelin that's been shadowing is behind that door attached to a body.
They enter and see someone sitting in a chair.
Fred: There she is.
Cassidy: It's over, Miss October Pest. Call off the bots.
Cassidy turns the chair, and the decomposing corpse of Abigail is there.
Shaggy: Like, that is worse than robots.
???: Nabiru.
Scooby: Did that thing just whisper?
Fred: I heard it, too. It sounded like...
Y/N: Nabiru.
Daphne: You think that was her name?
Velma: No. Her name was Frau Abigail Gluck. She was part of the benevolent lodge of mystery, the mystery-solving gang formed by Burlington in the 1880s. And when I got back from the Burlington library, someone had pinned a picture of another mystery-solving group on my wall... the Darrow family.
Daphne: Including us and the original Mystery, Incorporated, that makes 4 groups.
Velma: My guess? There's more.
Y/N: Almost as if this has all happened before.
Professor Pericles: Exactly right, Mystery, Incorporated.
They turn and see Professor Pericles and multiple robots.
All: Professor Pericles?
Professor Pericles: Ah! Lovely. I see you have met what's left of Frau Gluck. I met Frau Gluck in Bavaria in the 1930s. She discovered the missionaries possessed the fifth and the sixth pieces of the planospheric disc. She built this lab and a host of robots to aid her search for the pieces. I finally found this lab and continued the Frauâs work, building a legion of her Kriegstaufen robots to retrieve the pieces for me. My holographic masquerade as Frau Gluck bought my bots all the time they needed. And I would have gotten away with eliminating Cassidy if it weren't for you meddling kids. But it did give me time to take Y/N's piece of the planospheric disc.
Y/N went wide eyed and checked his pockets only for Professor Pericles to hold up his disc piece.
Y/N: Well, crap.
Professor Pericles: Now that I have everything I need, I can dispose of this place and all of you at the same time. Farewell, darling kinder. Farewell.
Professor Pericles then escapes as the robots advance towards the gang.
Cassidy: Time to go.
The gang runs as a female voice comes on.
Female Voice: Self-destruct in 10 seconds and counting.
Fred: We can't make it to Moby.
Cassidy: We got to try!
They all begin to run as the robots chase them. They slide down as Scooby catches Shaggy.
Cassidy: Look out!
Cassidy and Fred land on them.
Shaggy: Thanks, Scoob.
Scooby: Don't mention it.
They then make it back to the submarine.
Fred: We're leaving now!
Tub: I wish! Moby's stuck!
Tom: The only way we can leave is if someone stays behind and keeps the doors open with this manual override lever!
Cassidy: I'll do it.
Daphne: No!
Cassidy: I'll be right behind you. Trust me, I'm a fast swimmer. Go! I'll be fine. Go.
They all enter the submarine as Daphne looks at Cassidy.
Daphne: What we were talking about before, about regret... you weren't talking about me and Y/N. You were talking about you and Mr. E. You loved him once, didn't you?
Cassidy: What E. and I had, we lost a long time ago. I'm glad you and Y/N did not make the same mistake I did. Now, go!
Daphne enters as Cassidy puts on her helmet as the robots' approach and Cassidy pulls the lever releasing the submarine and the lab explodes sinking to the ground. The gang ascends to the top as they look for Cassidy.
Daphne: Do you see her?
Tom: Don't worry. She's here somewhere.
Scooby the seal comes up, barking.
Daphne: Look, gang. He's holding something.
The seal holds up the destroyed helmet of Cassidy.
Daphne: Oh, no! No, Y/N.
Daphne cries on Y/N's chest.
Y/N: It's okay. She must've gotten out. Right?
Shaggy: Like, yeah. Definitely.
Scooby: She saved us.
Velma: I guess maybe we were wrong about Cassidy.