The episode begins with Katie and Ryder watching a video of Mandy the Monkey, who was sick and being cared for by the veterinarian in the big city. Now that Mandy was better, she was being transported by train back to the jungle, but the train was making a pit stop in Adventure Bay, and Katie wanted to see how Mandy was doing.
At the station, Marshall and Rubble are with Mr. Porter, as the same train carrying Mandy was also delivering a fresh shipment of produce for Mr. Porter's store. Mandy is fast asleep in her car, but when the train screeches to a stop, Mandy is flung from her swing and woken with a start. The sudden stop also cracks the door to her car open slightly, allowing her to escape outside and watch the unloading of Mr. Porter's produce.
After getting her hands on a banana dropped by Mr. Porter and the pups, Mandy hears Katie and Ryder coming, and flees for the front of the station. When Ryder and Katie discover Mandy's car open and Mandy gone, Mandy finds Mr. Porter's van, full of fresh bananas from the train, and not only digs in to her primate nature's favorite fruit, but even drives off with the van as well. Katie is horrified, knowing Mandy can't be allowed to rampage through town, and Ryder assures her he and the PAW Patrol will get Mandy back to her car. He calls the pups, they head to the Lookout, and Marshall has his usually crash into the elevator.
The orders are clear: Find Mandy, retrieve Mr. Porter's van, and get Mandy back to her car for transport to her jungle home. Ryder deploys with Chase and Skye, and they set off to find Mandy.
Skye spots Mandy as she drives wildly and crazily around the City Hall. By the time Ryder and Chase catch up, Mandy has now driven Mr. Porter's van to where it is now locked on the railroad tracks, and another train is heading directly for her!
Chase tries to get Mandy to pull over, but gets a banana peel thrown in his face for his troubles. With the train getting closer, Ryder has no choice but to set his ATV to auto-pilot and commandeer the van from Mandy, steering it off the tracks just in time, and then bringing it to a stop.
Mandy, however, is still full of energy, and flees to the nearby playground, gaining the attention of Julius and Justina. Ryder and Chase try to lure Mandy down to catch her with a fresh banana, but the plan backfires, and Mandy, after giving Chase and Ryder a good raspberry for failing to catch her, flees once more on Ryder's own ATV.
While Chase resumes pursuit, Ryder gets a lift from Mr. Porter now that he had his van back, and find Mandy heading for the Lookout. While Skye provides over-watch, Ryder and Chase formulate a plan to finally catch Mandy. In the Lookout tower, Marshall is waiting for Mandy, but while Mandy enjoys the pillows and goes wild, Ryder and Chase arrive in the elevator and prepare for their plan. First off, Marshall seals the doors to the Lookout's balcony, trapping Mandy inside, and leaving her puzzled. Next, Ryder attempts to lure Mandy with another banana, but this time, he lures her into chasing it down the slide used by the pups to board their vehicles. Complete with a name call like the pups, Mandy goes down the slide, and lands in the back of Mr. Porter's van, where Mr. Porter and Katie close the doors and finally catch her. Ryder quickly reminds Mr. Porter to get in the driver's seat before Mandy gets there and steals the van again.
Back at the station, Mandy is back in her car, but now with a huge pile of bananas as well. As Mandy enjoys her meal, swinging back and forth with each time grabbing a fresh banana from the pile, the train departs to take her home. Katie, Ryder, and the pups see her off, and are happy she is going home. Mr. Porter soon joins them, his van now fully loaded with his fresh produce, but is upset that Mandy ate all the bananas. Marshall is upset due to his own love for bananas, but Mr. Porter reveals he salvaged enough of them for some fresh banana muffins. Understanding what Mr. Porter wants them to do to get one, Marshall begins acting like a monkey. After Marshall is rewarded and continues acting like a monkey, the others join in, leaving Katie, Ryder, and Mr. Porter to laugh at the pups and their "monkey business."