On the high seas, Cap'n Turbot and Francois are exploring once again on an azure day. As they explored on the The Flounder, Wally comes swimming in jubilantly for a treat from the duo. Cap'n Turbot notices his excited cries and offers him a bucket of squid jerky which disgusts Francois, making him comment that the squid jerky was "Stinky stuff". However, Cap'n Turbot replies that it was still Wally's favorite but Francois snatches the jerky from Francois and questions on whether Wally has eaten other treats before. He then drops the squid jerky onto the deck, making Wally displeased, and picks up a saucer of escargots, which is an Italian dish consisting of Snails. Cap'n Turbot eats the entire snail including its shell before being corrected that the shell was not supposed to be eaten and also comments that Wally should stick to squid jerky. However, Francois disagrees and the turbots began arguing over the small matter. As they argued over the small fit, the Flounder starts to rock violently, causing a broom and the food to go overboard. Cap'n Turbot suggests that it was Wally thanking them for the food but as the rocking stops, they both hear a loud bellow and also observe bubbles coming out from the depths of the sea. Francois then affirms that it was not Wally but a "Giant marine monstrosity" and suggests that they enter the diving bell to check it out. They do so coherently and drop down to the seabed. As they run to the window, they see a friendly Wally waving at them which confirmed that he was not the cause of the rocking. However, when Francois goes to the window on the other side, he spots a whale rubbing its body against the haul of The Flounder and runs to grab his camera. Cap'n Turbot questions on the whale's wiggly actions and Francois comments that it was probably just lonely and thinks that it was its mom. As he finishes, the whale spots the diving bell, rushes towards it, and starts rubbing on it instead, making it rock and the turbots uncomfortable. Francois screams to get out of the area and they both pilot out of the whale's way. However, it seems that the whale has taken a liking to the diving bell.
Meanwhile on Adventure Beach, Skye is busy posing for a picture being taken by Rocky. He then asks her for one more picture pose and she gets ready for it. However, as Rocky was about to hit the shutter, Marshall photobombs the picture, making Rocky comment that he already had many pictures of him. As he finishes, Ryder jumps in next to them and surprises them with Seaweed Pup-Treats given to them by Cap'n Turbot from his last trip. Rubble, who first thought it was liver flavored, then questions on the flavor and Zuma jumps down from his lifeguard chair, exclaiming that the seaweed was "Cool" and that it "Rules". Ryder then throws the seaweed pup-treats into Zuma, Marshall, Rocky, Skye, Rubble, and Chase's mouths and they all begin eating it scrumptiously. Chase comments that it was not bad a taste and Rubble mentions that it was salty and he liked it. However, as the pups finish their pup-treats, stains of seaweed remain in their teeth. Marshall, smiling, then asks Rocky for another picture but Rocky comments that he has seaweed in his teeth and giggles. Marshall notices the seaweed in his mouth and also jokes about it. Ryder asks all the pups to smile and they all smile and laugh at the same time, showing their teeth filled with bits and pieces of seaweed. Ryder then pulls out a box of dental floss and six toothbrushes and offers to brush them up.
Back in the diving bell, the whale continues to follow the duo. Francois notices this and panics, making him ask Cap'n Turbot on speeding up but he replies that it was not advisable. Without hesitation, Francois ignores his warning and accelerates the diving bell, causing both turbots to be swung back against the sudden forward thrust of the diving bell. As the diving bell speeds up, the whale picks up speed and does not let it out of its sight. Francois runs from window to window to check on where the whale was and it appeared to be everywhere to him, making Cap'n Turbot comment excitedly that it was actually circling them. However, Francois soon notices that the whale was nowhere to be found, making Cap'n Turbot conclude that the whale could have been worn out from swimming and has stopped chasing them. But unknown to them, the whale was actually swimming under the diving bell and without warning, it swims down and head-butts the diving bell out of the water, making it spin airborne and land upside down on the seabed. Realising their situation, Cap'n Turbot decides to call the PAW Patrol.
Back on the beach, Ryder finishes the last brushes on Marshall's teeth. Upon brushing, Marshall gives him a wide glamourous smile and Rocky offers to take a picture of him. Marshall gives a wide smile to the camera, but a seagull suddenly photobombs the picture as the shutter goes off, shocking both of them. As the seagull flies away, Ryder receives the call from Cap'n Turbot and accepts his call for help. He then calls the Pups to the Beach Tower HQ and they all do so with the usual Marshall shenanigans but with silly pictures being taken by Rocky's camera. After gearing up, Ryder begins briefing them on their mission. He deploys Zuma to use his submarine to distract the whale away from the diving bell and Rubble to use his underwater construction rig to flip the diving bell over. Ryder then asks Robo-Dog to load the needed vehicles into the Sea Patroller and they soon begin sailing to their destination.
When they reach their destination, they notice The Flounder but without anyone on it. Ryder concludes that Cap'n Turbot and Francois are nearby but Marshall comments that they are down below on the seabed, making Ryder decide on searching deep. He deploys Rubble and Zuma to get their underwater vehicles and the rest of the pups to follow him into the Sub Patroller. Rubble and Zuma jump into their vehicles together with Ryder and the pups entering the Sub-Patroller, all making their way to the turbots soon after.
As soon as their vehicles are in the water, Chase spots the whale on their left on the Sub Patroller's sonar, making Ryder conclude that the diving bell was close to them. Ryder asks Rubble and Zuma to follow his direction to find the whale. However, they report in saying that the whale found them instead. Upon observing the whale's size, Zuma exclaims how ginormous it was and they all follow it to find the turbots.
Meanwhile in the diving bell close by, the turbots notice Ryder and the pups and are overjoyed. As they rejoice, the whale bumps the diving bell once again, showing its presence to the turbots. Ryder gives Cap'n Turbot a call and reassures them that they are in good hands. Marshall then observes the whale and questions on whether the whale was trying to eat the diving bell based on its mouth being close to it. Ryder observes it closely and notices that its mouth was closed but was still blocking their way to the diving bell. He then asks Zuma to distract the whale away and he successfully does so. As Zuma and the whale play a game of underwater tag, Ryder asks Rubble to start flipping the diving bell. As he gets ready to do so, Wally comes in to help flip the diving bell but to no avail. Rubble thanks Wally for the help but mentions that it needed heavy machinery for the diving bell to be flipped.
As Rubble tries to flip the diving bell with light headed turbots, the whale continues to chase Zuma. But with a big push from Rubble's rig, the diving bell is brought upright. Cap'n Turbot thanks Rubble for the help and quickly asks Francois to pilot the diving bell out of the area. Whilst they do so, Zuma loses sight of the whale and questions to himself on where it is, but he soon finds it, but to his surprise, it was rubbing its mouth on a small undersea rock without stopping. Zuma reports this to Ryder and he asks Zuma to go in for a closer look. While close, Zuma notices that there was in fact something stuck in between the whale's teeth, making Marshall joke on whether the whale ate seaweed like them, with everyone bursting into laughter. Ryder then asks Rocky to help clean the whale together with him and Zuma.
When Ryder and Rocky reach the whale, Rocky calms the whale down and asks it to open its mouth. When it does so, Zuma notices that it was driftwood that was stuck in its mouth, and comments that it must be suffering for a bad toothache. Ryder inspects the teeth and suggests that the whale needed brushing and flossing, but Rocky immediately notices that they needed a bigger brush to do all those big teeth. As they think about what to do next, Wally swims in and suggest to Rocky that they could use the broom that went overboard from The Flounder to clean the whale's teeth instead. Rocky praises Wally and uses his claw to pick it up. With encouragement from Rocky, the whale opens its mouth and Rocky gives it a quick brush through. However, the driftwood remains stuck in its mouth. Ryder then suggests that flossing would do the job. Upon hearing him, Zuma swims to his submarine and pulls out his buoy rope from it. He then passes it to Ryder and Rocky and they begin to floss the driftwood out of the whale's teeth. They do so with minimal effort and Ryder praises the pups for their help.
Meanwhile in the diving bell, Francois notices that the whale was smiling and takes out his camera to get a quick shot, only to be dismayed by his hand blocking the whale in the picture. He then dismisses the matter quickly and says a goodbye to the whale. The whale then swims back into the depths of the sea, grateful.