Another beautiful day at Adventure Beach, and the beach is very busy as many residents are enjoying the beautiful weather and water. Everyone, except Mayor Humdinger and his Kitten Catastrophe Crew. Frustrated by how busy the beach is, Humdinger decides to attempt to clear the beach so he'll have it all to himself.
His first attempt with making it look like it's raining fails, and he's pretty much told off by Mr. Porter that he'll have to enjoy the beach with the rest of them, but after reprimanding the Catastrophe Crew, then whispering to them that he still loves them, he prepares his second plan: That being having the Catastrophe Crew man a mechanical shark to scare Mayor Goodway and everyone else off the beach with thinking that the water is dangerous as there are predators in the water. Though Chase plays it safe and orders the beach evacuated, as many citizens run for it, Mayor Goodway collects Chickaletta and leaves, while Mr. Porter ushers Alex away, but not without both Porters turning an angry glare towards Humdinger, suspecting foul play from him. Cap'n Turbot and Ryder are skeptical and suspicious of there being sharks, and on Cap'n Turbot's suggestion to investigate, Ryder summons the pups to the Sea Patrol HQ for briefing on their mission. Once there, Ryder assigns Marshall and Skye to help with dealing with the shark, and once their Sea Patrol vehicles are loaded up, the Sea Patroller sets sail to deal with the threat.
Once at the beach, Skye, Marshall, and Ryder get to work dealing with the Catastrophe Crew's shark. Skye takes to the air in her seaplane to look from above, while Humdinger watches from the beach. Pleased to see the Sea Patroller heading for open water, he contacts the Catastrophe Crew and tells them to keep the PAW Patrol away from Adventure Beach for as long as possible, much to the kittens' annoyance at how long they'll have to keep up this ruse. Ryder and Marshall launch out of the Sea Patroller once Skye spots the shark's dorsal fin, and once they catch up, Ryder loads up the water cannons on Marshall's fire boat with treats in a bid to lure the so-called shark away. However, after Marshall fires off two salvos, the Catastrophe Crew don't bite.
However, when Cat Rubble gets tired, the kittens nearly expose themselves as they turn the shark back towards Adventure Beach, forcing Ryder to have Skye make sure the beach is still empty. Spotting Skye, Marshall, and Ryder heading his way, Humdinger orders the Catastrophe Crew to get the shark away from the beach, and Cat Rocky takes over for Cat Rubble with steering it away. However, the Catastrophe Crew's frantic attempts to keep the pups busy and away from Humdinger results in the shark beginning to flood. Chase and Rocky head down in Rocky's underwater transport to finally discover the truth, but before they can help the kittens, they panic and drive the shark onto the beach and after Humdinger. Skye had spotted him earlier and had managed to warn him in advance, causing him to run for it before Skye manages to get him to safety with her vehicle, while Ryder and Zuma arrive on the beach, with Ryder converting his ATV back to its normal vehicle mode as he makes landfall alongside Zuma's all-terrain boat, and Zuma manages to finally bring the shark to a stop, before the Catastrophe Crew stumble out of the shark in tired exhaustion, exposing Humdinger's plan to have the beach all to himself.
With the truth exposed, Humdinger is reduced to handing out towels to everyone as they return to the beach, and the shark is used by the pups to allow people to water-ski.