It's Halloween in Adventure Bay, and the pups are busy with getting everything ready for the celebration at the Lookout. Ryder helps Skye with her costume, Chase works the decorations, and Rocky and Rubble work on a very large jack o' lantern.
Meanwhile, over at the dock near the beach, Cap'n Turbot is preparing to take Mayor Goodway, Chickaletta, Katie, Cali, Mr. Porter, and Alex on a haunted ghost ship ride. Cali however, is angry at how Chickaletta is wearing the same costume as her, but Chickaletta is not bothered by it. The other costumes have Cap'n Turbot wearing a squid on his head, Katie as a witch, Mayor Goodway dressed as a ladybug, Alex as a frog, and Mr. Porter as a clown.
At the Lookout, the pups are scared by Marshall as he appears in his pumpkin-themed costume for going trick-or-treating. Each of the pups are dressed up differently: Rocky as a Viking, Skye as a princess, Chase as a superhero, Zuma as a pirate, and Rubble as Elvis. Ryder is dressed up as a knight so he can go trick-or-treating with the pups as well.
Back at the dock, trouble is brewing on the ghost ship. Wally keeps snatching the Halloween cookies Mr. Porter baked up right out from under Mr. Porter and Mayor Goodway's noses and devouring them when they aren't looking, and Cali raises the sails by accident chasing a seagull. Soon the ship has set sailed, and Cap'n Turbot loses his glasses attempting to swim after it to catch up. Chickaletta unknowingly keeps steering the ship as she jumps back and forth on the ship's wheel due to being amused by it turning back and forth on its own, which also causes the ship to sway as well. Mayor Goodway does her best to maintain confidence and no belief in ghosts, but a mysterious groaning has her freaking out anyhow. Mr. Porter decides the only option left is to call the PAW Patrol, and phones Ryder as the pups are continuing their trick-or-treating.
When Ryder gets the mayday call, he calls the pups to the Lookout, where Marshall crashes into the other pups like bowling pins. Marshall tries to make light of what happened with a couple of jokes, but none of the pups laugh, forcing Marshall to flat out tell them that they should just get topside and get their orders before the pups chew him out for his puns. That decision the pups don't argue with and are all smiles afterwards as they head up. When they're suited up, everyone, except for Skye, are still wearing the headgear for their costumes. Skye had to switch her princess hat for her pilot's cap and goggles.
When they arrive, Ryder passes out the following orders: Marshall will be airlifted by Skye to the ship to lower the sails, while Zuma joins Ryder with catching up on the water. The team deploys, and despite him still wearing his costume, Ryder is still able to deploy his life jacket underneath his armor before he and Zuma hit the water, without causing any damage to either his costume or his life jacket.
When they catch up to the ship, Skye is able to get Marshall into the crow's nest, allowing him to lower the rear sail, but there's still the matter of the ship's rocking caused by Chickaletta working the ship's wheel. Ryder manages to grab hold of the ladder after setting his ATV on auto-pilot, but Zuma is unable to jump the distance from his hovercraft to grab Ryder's hand and falls into the water. He manages to recover via his Pup Pack and rejoin Ryder to resume climbing aboard. Once Ryder, Marshall, and Zuma are aboard the ship, it is not long before they find the sources for the ship being so-called "haunted":
They find Chickaletta manning the ship's wheel and recover her, ending the ship's swaying.
The eerie groans coming from behind some barrels was actually Wally the Walrus, having dozed off after pigging out on Mr. Porter's Halloween cookies.
When one of the sails is raised again by Cali's attempts to catch a seagull once more, she's caught red-handed this time, much to Katie's bemusement.
As for Cap'n Turbot's missing glasses, Ryder soon points out that they're in his back pocket. With the mysteries solved, the ship is brought back to the beach and properly moored so it doesn't take off again. However, before everyone can enjoy the party, more eerie moaning convinces everyone to abandon ship and refuse to go back aboard, faking seasickness to get the pets and Alex off. Luckily, Ryder convinces everyone to return to the Lookout to have their party there instead.
Back at the Lookout, everyone enjoys themselves. Ryder gives the pups some of the cookies that Wally did not eat, Alex plays Pin the Tail with Katie and the adults, and Rocky and Zuma spook Skye as she asks about where her prince is. Everyone is enjoying themselves until Rocky sees something and howls at the moon, leading to the rest of the pups doing the same, as they notice a ghost version of the ship floating through the sky. Everyone is amazed, if not a little spooked, and are truly in awe over the excitement they all had for Halloween, be it either trick-or-treating, solving a mystery on a ghost ship, or even seeing a real ghost ship as it floated across the night sky in front of the full moon.