A rock slide has trapped Katie and Cali on a train on the old trestle bridge! Ryder and the PAW Patrol have to clear the tracks and free the train before more boulders tumble down.
The episode begins with Chase and Rubble hard at work with the sand pit outside the lemonade stand on Main Street. As Rubble finishes smoothing out the sand, Alex and Precious' Owner ask for a sand castle, but Rubble chooses to create a sand replica of his digger instead. While Alex and Precious' Owner argue over who will play 'Rubble' with the sand digger, Chase and Rubble share a laugh over Rubble's love for being a construction pup.
Elsewhere, the train is on its way to the station in Adventure Bay. On board, Katie and Cali are enjoying the ride as they return from Katie's grandmother's house. Cali's stomach is growling, indicating she's hungry again, but Katie refuses to share any of the treats from her grandmother, as they are for the PAW Patrol. Cali's stomach growling soon gets louder, but a very loud rumble scares Cali, and even Katie. In the locomotive, the engineer sees something ahead and engages the emergency brakes. It's soon revealed that a rock slide has occurred. Worse, one of the larger boulders rolls down, and smashes into one of the wooden support beams for the railroad bridge that the train is now stranded on, cracking it and weakening it. If it gives out, the bridge will collapse, with the train going with it. As the engineer tells Katie what happened, Katie calls Ryder to let him know.
At the Lookout, Ryder is busy playing video games on the Pup Pad, when he gets Katie's call. Wanting to make sure, he looks through the Lookout's periscope towards the bridge. Once he sees the problem, he lets Katie know the pups are on their way, and summons them to the Lookout. Marshall manages to enter the elevator without a problem, but all the other pups come crashing into him. When they reach the top, Ryder tells them of the situation, and a replay of Katie's call worries Skye, but Ryder assures her they will get Katie and Cali home safe.
Rubble and Rocky will come with Ryder up to the bridge to clear the rocks away, while the other pups remain at the Lookout as backup.
When Ryder, Rubble, and Rocky arrive at the blocked track, while the pups get to work with the cleanup, Cali slips away from Katie to go after a bag of potato chips that a seagull was eating on the roof of the train. After faking out the seagull twice, Cali pounces, but misses, and the bag and chips fall into the river below, much to Cali and the seagull's sadness.
Meanwhile, Ryder goes to check the bridge, and discovers the damaged support beam. He asks Rocky if he can come down and help, but it is too steep for his truck. Knowing they need more help, Ryder calls Chase and asks that he will bring his winch to help with stabilizing the support beam until the train is off the bridge. While Chase soon arrives and lends his winch to lower a large log down to brace against the crippled support beam, Cali sees another chance for some food when the seagull returns with a loaf of bread to munch on. Cali scares the seagull off, but it returns and takes the bread with it, leaving Cali still hungry.
Meanwhile, the rock slide is cleared and Ryder gives Katie the okay to let the engineer know he can start the train again. Katie agrees, but then mentions her worry for Cali.
As the train starts, Cali is unable to grip the roof, and is sent tumbling until she is grabbing the edge of the roof of the carriage for her dear life. As she meows in fear and fright, Ryder and the pups hear her, and Chase]] leaps into action. Using his canine agility to climb up the front of the locomotive and onto the roof, Chase soon finds Cali and helps her to safety. As Cali hugs Chase in gratitude, Chase lets off a sneeze due to his allergies, but endures it, especially when Cali is scared into his arms again by the train whistle/horn blowing. Cali is soon reunited with Katie, who thanks Chase for all his help, and despite nearly falling off the train himself due to another allergy-induced sneeze, Chase assures it was all in the line of duty.
Later, back at the Lookout, Katie rewards the pups with the treats from her grandmother, but Cali still attempts to sneak one herself due to still being hungry. In the end, Chase offers part of his that he didn't eat to Cali, and all is well, save for Chase knocking over the other pups with another sneeze due to his allergies.
As the pups and Cali play, the Seagull reappears, now munching on a jelly doughnut. Cali attempts to climb up the slide to get it, but the slippery surface prevents her from doing so, and Chase soon joins her when trying to retrieve the soccer ball. In the end, the Seagull shows it has a good heart, and tosses the doughnut to Cali, only for it to land on her head, and leave Chase on his back, laughing at Cali's misfortune as the episode ends.