After Marinette's confession to Luka, Adrien knew this would happened, he wouldn't let Luka win.
Adrien: That's it! If you want something done, you gotta do it yourself. *In Hawkmoth's Lair, the window start to open and butterflies start to flutter all over the place.*
Gabriel: Hmm. Looks like anger has strikes again. Let's get to work. *He moved his tie, but there was no Butterfly miraculous.* What the? Where's my miraculous? Nooroo! *He looked around and he scowled.* NOOOOOOOOOOOOOOOOO! Who did this? Who took my miraculous?!There's gonna be hell to pay when I find out who took it from me.
Outside, Adrien was fumed with anger at them both.
Adrien: (You're blowing off the deal, Marinette. Prepare the maximum punishment you're gonna get when you at least expected. *He stomped away in anger. But what they didn't know is that something was bubbling underwater, well two things.*
Marinette: Promise me nothing will never happen again?
Luka: I promise. *He hugs her.* (She's too worried and afraid of all that's going on.) *Soon, they felt a small rumble.*
Marinette: What was that?
Luka: I don't know. Stay here. I'll check it out. *He see a swarm of bubbles in the water.* (What the?) *Soon, something splashed out of the water, it was a giant Sea Serpent monster, Luka fell back.* Marinette, go inside where it's safe.
Marinette: What?
Luka: Just go. I can handle this one.
Marinette: Okay. *She go inside the houseboat where it's safe. The Sea Serpent roared again, Plagg came out and he screamed.*
Plagg: What is that?
Luka: A Sea Serpent. We gotta go.
Plagg: I hate transforming.
Marinette: I have to go out there.
Tikki: Luka said stay here.
Marinette: You don't understand. I have to do this, please?
Tikki: Okay. *Soon, the Sea Serpent roared and he caught Luka and swim underwater.*
Marinette: Luka, no! *She run outside and she doesn't see him anymore.* Nobody messes with who I belong to. *She get out a blue macaroon.* Tikki, power up! *She threw it up and Tikki ate it and she start to transform.*
Tikki: Aqua Tikki.
Marinette: Aqua Tikki, spots on! *She transform into Aqua bug, she opened the window and dive in the water. In the water, Luka gets deeper and deeper in the water, Plagg saw it and he tries to help him out, but he can't.*
Plagg: Come on, Luka. Where are you, Ladybug?