Marshall dreams that a shrink ray miniaturizes himself and his fire engine, and the teeny-tiny pup goes on a big adventure in his own backyard. Ryder and the pups have to be very careful to rescue little Marshall without stepping on him.
While the pups play, Rocky and Ryder are building a new invention in front of the lookout, and when Marshall asks them what it is, they tell him it is a surprise invention, and refuse to tell him in fear of spoiling it. Marshall is then called back by the other pups, and as they finished their game, the ball falls down a gopher hole. Marshall gets his paw stuck trying to get it out, and though Skye and Zuma help free him, his team loses the game. He then heads off for a nap in his pup-house after some comforting words, and falls asleep as Ryder and Rocky continue inventing.
Marshall is then woken up by the lost ball and the gopher who lived in the gopher hole. He gripes to Marshall about the ball, and to Marshall's surprise by actually speaking, something the gopher attributes to as having nothing important to say beforehand. As he chases the gopher, he steps on the ball and rolls into Ryder and Rocky's invention, which fires a beam that shrinks his pup-house and the ball. As Marshall observes the results, a passing crow lands on the invention and causes it to shrink Marshall out of his pup-tag, though while surprised, Marshall quickly begins enjoying himself, and he sets off exploring the world of the small in his fire truck. After racing a few laps around some toys, he encounters a group of ants with the shrunken ball, and begins to follow them to get it back.
When the other pups go to find Marshall for another ball game, they find themselves surprised when they see that both Marshall and his pup-house are missing. Chase then has Zuma try calling his pup tag, only for Rocky to find it where Marshall's pup-house usually sat. Rocky then realizes that the shrink ray is uncovered, and all the pups then realized that Marshall may have been shrunken, which is confirmed when Chase finds tiny tire tracks leading into the grass. The pups quickly alert Ryder to the situation.
As Marshall drives through the grass, having lost the ants, he marvels at the size of the grass. He then decides to call Ryder to help find his way home, but finds he is missing his pup-tag. This doesn't deter Marshall, and he continues into the grass to find his way home.
Ryder is quickly alerted to the situation by Chase, and as all the pups run towards the elevator, Marshall hears the commotion and attempts to join in, but his truck hits a squeaky toy and is sent flying into the grass, forcing Marshall to look with disappointment as his friends go on a mission without him. Ryder then selects Chase to search for Marshall with his drone and Rubble to pick up Marshall's truck with his electromagnet, allowing the search to begin. Chase and Rubble quickly comment about the shortness of the ride.
As Marshall makes his way to the lookout, he hears the caw of a crow, which quickly begins to try and catch him. As Rubble activates his electromagnet, Marshall abandons his truck and hides under a toy boat, eventually resorting to scaring the crow away with his water cannons. Rubble eventually grabs his truck, though unfortunately, he pulls it away without Marshall in the driver's seat. This forces Marshall to begin a long walk home, and when the others find Marshall still missing, they send out Chase's drone.
Passing an anthill, Marshall helps out the ants by pushing a strawberry with his water cannon. They thank him by giving him the ball back, and putting it in his pup-pack, Marshall scales the anthill only to bemoan that he is still too far from the lookout. Fortunately, he is spotted by Chase's drone, and with the ants' help, he catapults himself up with a blade of grass and mounts the drone. Unfortunately, this puts him out of the drone's sight, and the others decide to try and look for him with the lookout's periscope. Chase recalls his drone doing so, sending Marshall flying off into a water dish. He then enters the elevator with the others, but to his disappointment, neither Chase or Rubble notice him with them, and they couldn't hear him shouting to them.
As the other pups begin searching for him, Marshall has a brainwave and puts it into action, using his truck's ladder to call the others via Ryder's pup-pad, allowing them to finally see him. Unfortunately, his celebration jump sends the pup-pad tumbling onto a pillow and he is sent bouncing down the slide, forcing Skye to give chase before he crashes. She eventually catches him, and as Ryder readies to shrink ray to turn him back to normal, Marshall wakes up, revealing it all to be a dream. After some confusion, Ryder reveals that he and Rocky were building a floodlight to let the pups play late at night. Chase then fires a ball, which once again accidentally rolls into the gopher hole. The Gopher then holds the ball disapprovingly, and after some questioning looks, all the pups laugh after Marshall reveals the talking gopher portion of the dream.