As the pups are enjoying themselves outside The Lookout, Ryder soon calls them to let them know it's time for bed as it's getting dark out. Rubble only returns to his pup house as night falls due to his fear of the dark and spooky things.
However, Ryder is soon awoken by a call from the Earl of Barkingburg, who is very frightened as he mentions that the Princess of Barkingburg thought she saw a suit of armor that might mean the castle is haunted. Seeing that the Earl could use the PAW Patrol's help, Ryder summons the pups to the Air Patroller.
Once all the pups are on-board, Ryder explains what they are up to, which the pups immediately realize is a Mission PAW because they are heading to Barkingburg again. Robo-Dog puts the Air Patroller into stealth mode, and the team rocket away to Barkingburg at Mach 1. Once there, the Air Patroller lands in the Mission PAW command center, the pups and Ryder suit up, Chase joining them this time compared to the first Mission PAW, and once Ryder selects Chase and Skye for the mission, the Mission PAW Cruiser is loaded up with the mini-vehicles, and the team heads out to Barkingburg Castle.
When they arrive, the Earl emerges with the Butler of Barkingburg Castle and Sweetie, very scared. However, the Princess is excited and wants to find the ghost. While Ryder, Chase, and Skye go with her, the rest of the pups stay with the Mission PAW Cruiser and the Earl. Rubble wants to join them, but quickly loses his nerve after a short bit and returns to the cruiser.
Unknown to anyone, Sweetie is behind the haunting in another attempt to become Queen, this time to have the castle all to herself, using her chew toy Busby to control the stuff around the castle by remote control. When Skye is about to discover the remote control device on the suit of armor when they chase it down, Sweetie summons three more to stop them. However, they still discover the control device, and after Sweetie and Skye fight over control of Busby, it causes the microchip allowing Sweetie control of the suits of armor to fall out of Busby and short out. However, the armors keep coming, forcing the Princess to open a secret passageway for everyone to escape through. After the Princess, Ryder, Chase, and Skye escape, Sweetie puts the castle on lockdown, thinking she's won, until she sees the suits coming after her, and upon realizing that Busby can't deactivate them, Sweetie calls Ryder on his wristwatch Pup-Pad to tell him of the situation.
Ryder calls Rubble back at the Mission PAW Cruiser, but despite Rubble being nervous about the haunting, he overcomes his fear to break into the castle with his mini-miner and take out the suits of armor, saving Sweetie. However, once it is revealed that Sweetie is behind the haunting, Sweetie tries to avoid punishment by saying it was in good fun, but while the Princess is not cross with her, she still confines Sweetie to her doghouse anyway, much to Sweetie's chagrin.
With the situation resolved and Sweetie punished again for her actions, the Earl and Princess thank Ryder and the pups for their help. Following some chatter regarding Rubble and conquering his fear of ghosts and the dark, everyone shares a good laugh.