A few days after the defeat of the Sapotis, Ladybug and Cat Noir met for a patrol. Cat Noir was visibly a little angry.
- What's wrong kitty?
Cat Noir coldly looked at Ladybug, looked away and then answered.
- If you don't want us to be together, just say it. Ever since I asked you back when we thought Glaciator and you've kept avoiding it ever since. It's fine if you say no, the only thing I ask is for you to be honest with me.
- Of course I want to be together with you, you're such a good and supportive partner, you're always there by her side but I'm afraid that if Hakw Moth found out he would use it to hurt us, and I couldn't bear to see something bad happen to you.
- But how could Hakw Moth find out? I'm sure we can make it work it's going to be you and me against the world.
Ladybug remains silent. She looked at Cat Noir who was giving her a sweet smile. She teared up before hugging her partner tightly.
- Always...
Cat Noir returned the hug. They remained like this for a while before eventually Ladybug continued.
- My answer is yes, yes I will be your girlfriend Cat Noir,no matter what happens we'll get through it together.
Right as Ladybug finished, screams could be heard on the streets. The duo, now a couple looked down and saw a couple of panthers had escaped the zoo.
- Well, that's a CATastropie.
-Let's try catch them.
Ladybug jumped down and caught one of the panthers with her yo-yo but it was running so fast that even the yo-yo couldn't stop it,so Ladybug was water skiing on asphalt.
- AAAAH, I CAN'T STOP IT!
- Hold on my lady.
Cat Noir jumped right on the panther and tried taking off the yo-yo but he got thrown off and bumped into a poster with Adrian's face.
- What are you laughing at?
Eventually the panther reached a corner and turned, giving Ladybug the opportunity to detach the yo-yo from the running panther.
- OK, time for a different approach.
A few minutes the panthers were caught in a van with the help of Rena Rouge's mirage.
- Nice work. Pound...
Ladybug left with Rena Rouge without even fist bumping with Cat Noir.
- Hey, where are you going?
- Rena is about to detransform.
- So you get to know who she is but I don't?
Rena Rouge's miraculous beeped.
- We really have to go now.
- Go ahead, I'll be right behind you.
Rena Rouge jumped down the roof leaving Ladybug and Cat Noir alone.
- I know you feel excluded and trust me I know how it feels. I will talk to him and if he agrees...
- Who is "him"?
- I... I don't have time right now but I'll tell you, I promise.
Ladybug left Cat Noir all alone on the roof. He left out a sad sight before leaving as well.
-We can do this again whenever you want, Lady...
Alya's phone rang.
-Oh! The movie!Bye !
Alya left waving goodbye. Ladybug detransformed as well and ran the opposite direction.
-Uh, if you want to get to that movie on time too, you better go the way Alya went.
-Sorry, Tikki; we'll just have to miss the trailers again.
Meanwhile at the swimming,Kim was playing a game with his friend, Ondine,truth be told though, Ondine didn't see Kim as just a friend. She admired his courage and charismatic style.
- "I can stick my big toe inside my ear"...?
Kim demonstrated his hidden talent making Ondine laugh. Kim gave her the notebook and pen with his feet.
-Let's stop beating about the bush.
Ondine noted something down and threw the bracelet she put the paper in into the pool. Kim dived in, retrieved it, and started to unfold the paper, but then his watch alarm went off.
-Ah! The movie! I totally forgot!
-But we haven't finished yet!
-I've really gotta split. I asked Chloé to come, remember? The girl I told you about in my class? Next time, I promise!
Kim left. Ondine reached out toward him, then picked up the paper and openex it, revealing a heart with Kim's name on it, and "Je t'aime" written below, with more hearts.She sat down and started crying. Suddenly an akuma entered the pool and into Ondine's bracelet.
-Syren, I am Hawk Moth. I'm giving you the power to turn Paris into your own underwater kingdom, for you and your prince. In return, you must bring me Ladybug and Cat Noir's Miraculous.
-May they all sink under my sorrow.
Ondine transformed into Syren, and stood up. Her tears falling into the pool triggered the water to rise up and overflow the pool.
Meanwhile in Master Fu's shop, Marinette brought him back the fox miraculous. He put it into the miracle box and then put the box back into the gramophone.
-Perfect. Now come and tell me what's bothering you, Marinette.
-Huh? How do you...?
Master Fu laughed as he was leading Marinette into a different room of his shop. Tikki and Wayzz were always curious to see what was there but they were never allowed to. They tried following their owners into the room but Master Fu stopped them.
-Hold on. You both stay here.
- Oh, Master please!
- I am sorry but you know the rules, kwamis can not know the contents of the miraculous book. Imagine what would happen if one of you were captured by a villain, just like Hawk Moth's kwami, Nooroo.
- Ooh!
Wayzz and Tikki got scared and flew away into the mattress. Marinette and Master Fu entered the room.
-So, what's on your mind, Marinette?
- Well, I feel bad for keeping so many secrets from Cat Noir.I don't want to leave him in the dark.
- Tell me, Marinette; do you put the noodles in the water before the water boils?
- Mmm... no.
- Exactly. That's because there's a right time for everything
Master Fu poured a cup of tea and gave it to Marinette.
- Anyway, what did you want to show me in the book.
- Well you remember how I told you the book can help us unlock new powers for your miraculous? I believe I might have finally found out how.
- Wow, really? That is amazing!
- Yes, indeed it is.
Master Fu showed Marinette a page from book on his tablet.
- A long, long time ago, when Tikki, the kwami of came on Earth, some of her magic fell in five different places creating three pearls and two stones which can give the ladybug miraculous new powers. The exact location of these jewels was unknown, until now. The locations are written in the book.
- Great, then we can go look for them!
- It won't be that easy, the locations are written down as riddles. Furthermore the book was written a long time ago so there is no guarantee the riddles are still accurate.
- We could at least try. What kind of riddles are there exactly?
- Well,as an example, the riddle of the pearl of the sea is as follows:
"To find that you seek,
Dive deeper than the deep,
Where water flows though the heart
Where darkness hides away the light"
Marinette was puzzled by the riddle.
- It probably is a river, but there are thousands of rivers in the world! How can we know which is the right one?
- This is the problem, we can't.
- I am sure there is a way so we can't give up!
Marinette's phone rang.
-Hey Alya...yeah, what's up? The movie? Oh, uh, of course I didn't forget. I'm almost there.
Marinette hung up and ran out the door.
- Sorry Master, I'm sure we'll figure it out!
A little later Marinette finally arrived at the cinema.
-Coming! Sorry, I was-
-No time to explain. Come on!
Alya and Marinette ran inside and occupied their sits. The movie started to play.Suddenly, people in the frontmost row got up and run out, followed by people in rows succeedingly further back doing the same.Water rushed under the seats where Marinette was sitting. She, Alya, Nino, Max, Kim, and others in that row lifted their feet onto their seats. Out in the streets, people screamed as flooding water raged. Water also rushed into the theater.
-Okay, who left the faucet running?
-The stairs! Quick!
People ran upstairs toward the roof, with water flooding the stairway right behind them.Meanwhile in the Agreste Mansion, Adrian was trying to make Plagg tell him what Ladybug was hiding.
-You must know what Ladybug's hiding from me, Plagg.
-I'm just a kwami, Adrien, and we kwamis have a right to remain silent.
-Pity. Just when I was about to order you some very tasty cheese. Have you ever sampled La Trappe d'Échourgnac? It says here it tastes like walnuts.
-I can't be swayed, sorry.
-Did you know about the Fourme de Montbrison? Apparently, it's the oldest cheese in the world.
-You don't say...
-Yes...and do you know why its rind is orange? Because they age it on special boards of spruce wood.
-There's only one thing in this world that smells as good as cheese.
Plagg flew off into the bathroom into Adrian's basket with dirty clothes. He got out a dirty sock and starting breathing in out it.
-Which one do you prefer, the Tomme de Bouche, or the Saintignon?
Plagg let out a loud scream of fury.
-Tome de Quraish with truffles; raw milk Camembert, aged on vine leaves marinated in Emmental juice.
Adrian stopped when he realized his room was being flooded.
-Looks like your whole cheese strategy will have to tread water.
-Don't worry, this isn't over.Plagg, Claws Out!
Adrian transformed into his superhero alter ego Cat Noir and left his room. Meanwhile the water almost reached the cinema's rooftop.
-My circuits are sensitive to water.
-Wha, ho, ho, ho! Ha, ha!
-Come on, guys! I can teach you to swim in two seconds flat, Markov. You just put your arms like this, then you push your legs, and it's kind of like being a frog, you see. In fact, it helps to think as a frog, too, you know...
A fin could be seen approaching in the water. Syren leaped out and dived back in, pushing Kim underwater with her.
- Kim!
Marinette quietly slipped away and tried to get away from the rooftop using a trash bin as a boat.
-Where is he? Can you see him? Marinette, what are you doing?
-Um, I'm gonna go get help!
Marinette paddled out of the other's sight.
-Okay, we're alone.Tikki, Spots On!
Ladybug dove into the water and swam around.Paris was now an underwater kingdom. She was nearly swallowed by a giant catfish, but dodged it, and then surfaced. She took a deep breath and went back underwater. She spotted Syren pulling Kim along with her.
-Huh! This is amazing! I can breathe underwater, just like a fish.
-I knew you'd love it, and I've got lots of other surprises for you, you'll see...
Ladybug grabbed Kim with her yo-yo, and pulled him back away from Syren.
-Hey!
- My prince!
She swam after Kim, grabbed him, and pulled back him and Ladybug, who grabbed hold of a window railing to stop them as she ran low on air.
-With every new environment comes a new set of rules, Ladybug, you won't be able to win this time. Ladybugs can't breathe underwater. Syren, are you going to let Ladybug steal your prince away from you?
- Never!
Ladybug tried to swim up so she could get air but Syren grabbed her foot so she couldn't. With every second Ladybug started becoming dizzy from the lack of oxygen and slowly started losing consciousness. Suddenly her vision blacked out and the next thing she knew,she was on a rooftop with Cat Noir.
- What happened?
- Syren tried to hold you underwater so you couldn't get air but I managed to get you out in time. Are you ok?
- Yeah, I am fine, don't worry but we have to save Ki... I mean that boy and Paris.
- Yes but how? We can breathe or swim in the water like Syren does!
Suddenly Ladybug's earring started glowing. It was emanating a blue aura.
- Wow,look at your earrings, is it normal?
- Huh?
Ladybug saw the reflection of her earrings glowing in the water and she remembered Master Fu's riddle
- Well of course. I know how to defeat Syren but I have to dive to the bottom first.
- Mmm...why?
- You'll understand.
Ladybug tied wrapped her yo-yo around her waist and gave Cat Noir the end.
- If I pull by the string, get me out.
- OK, but please be careful.
- I will
Ladybug gave Cat Noir a kiss on the cheek before taking a deep breath and jumping in the water. She swam and swam, deeper and deeper and it was becoming darker and darker. She eventually got there the Seine used to be and saw a glow at the bottom and her earring started glowing brighter. She swam towards the glow and underneath the sand she found the pearl of the sea, which was glowing the same colour as her earring. Syren saw Ladybug.
- I got you this time!
The villain swam as fast as she could towards Ladybug. On the surface, the end of Ladybug's yo-yo magically disappeared from Cat Noir's hands.
- What?!
He looked in the water in hopes to see what was going on but he couldn't. Suddenly a Ladybug with a blue costume jumped out of the water followed by an angry Syren.
- Wow.
-I knew those Miraculous had hidden powers! Syren! There's too many fish in this sea. Take their Miraculous before they take your merman away in their net!
Ladybug, now Aquabug, and Syren jumped back in the water.
- You will never take my merman prince from me!
Syren charged towards Aquabug but she swam up and kicked Syren with her foot from behind sending her into wall.
- We don't want to separate you, we just want you to bring you back to normal.
Syren groaned before swimming furiously past Aquabug towards the pool. Aquabug swam back up to Cat Noir.
- Nice new costume.
- Um, thanks.
Aquabug got out of the water.
- I don't think I can defeat Syren alone.
-Cats aren't exactly crazy about water either, you know. Is there any chance you can get us a submarine?
-Pawssibly, kitty cat. Aqua Lucky Charm!
Aquabug got a car key.
- Mmm... ok here's the plan.
Aquabug explained the plan to Cat Noir. Meanwhile Syren arrived at the pool where Kim was sitting in a throne protected by a bubble.
- I love what you've done with the pool! It's awesome!
-This is the pool where the old me tried to pour her heart out to you so many times.
-But, uh...I've never seen a Syren at the pool.
Syren held up her wrist with her swimming bracelet for Kim to see. Kim stared at it for a moment until he recognized it, and gasped.
- Ondine ?!
- I'm your Syren now. And you could be my merman. It only needs a kiss, and you'll become just like me!
- You mean I could swim as fast as you?
Syren took Kim's face in her hands, and stared to pull it face toward hers.
-Yes, Kim! You'll be my Prince, and we'll rule this underwater city together, forever!
Kim puckered his lips until a thought crossed his mind.
-Wait! Does this mean I never get to see Mecha Monkeys vs. Cyber Sharks 3?
- What?
- Oh, yes you will, don't worry! In fact, you'll probably make it to the next showing!
Syren charged towards Ladybug but she swam away towards Kim.
-Tell me, what happened to your friend that got her so worked up?
-We were playing a game of secrets, and I think she was trying to tell me that I'm the boy she likes. But, I was a doofus and didn't realize.
-Game of secrets? What kind?
-It's a game Ondine invented. You write down a secret and put it inside the bracelet's capsule. It's awesome! You wanna know my secret?
-That's where the akuma must be!Here. You can breathe through this.
Aquabug gave Kim her yo-yo so he could safely get out of the bubble. They started swimming away.
- Kim!
Syren swam after Aquabug and Kim but she lost them. Eventually she spotted Aquabug.
-Ladybug! What have you done to my prince?!
- I think he took someone else to the ball.
Kim was hiding with Cat Noir behind a chimney. Aquabug talked to Cat Noir through her ear communicator.
- Be ready to strike!
Aquabug swam along until she swam through a car with its doors open on both sides, Syren following until she entered the same car.
- Cat Noir, now!
Cat Noir used his stuff from the surface to hid the car and trigger the airbag, pinning Syren inside.
Aquabug closed the doors of the car and locked it using the key. She then tied the loop-end of her yo-yo around the car's trailer hitch, and she swam to the surface.
Aquabug leaped out of the water, and landed the roof where Cat Noir and Kim were. Aquabug wraps her yo-yo around Cat Noir's staff, which he then extended, and pulls on like a fishing rod.
-Looks like I got a nibble! How cool! I always wanted a goldfish!
Aquabug unlockef the car with a key signal. Its door pops opened, spilling out water. Ladybug reaches inside, takes Syren's bracelet, and cracks it in her hands, releasing the akuma.
-No more evil-doing for you, little akuma. Time to de-evilize!
Aquabug caught the akuma with her yo-yo and purified it.
-Gotcha! Bye bye, little butterfly. Miraculous Ladybug!
The miraculous wave brought everything back to normal.
A while later, Ladybug was on a rooftop near Master Fu's shop with Cat Noir.
- I am sorry I have to keep secrets from you.
- I understand that keeping our identities secret is important to protect those we love but who were you talking about earlier?
- This is why I brought you here.
Ladybug jumped down from the roof and Cat Noir followed her. They were at the back door of Master Fu's shop. The old man came out the door smiling.
- Huh?
- Cat Noir, meet Master Fu, the guardian of the miracle box.