At first Stan Marsh and Dexter Cavanaugh didn't get along easily, in fact, they used to get on each other's nerves, mostly Dexter would get on Stan's nerves, a lot.
In a world where toys are living things who pretend to be lifeless when their owners are present, a group of toys owned by a six-year-old boy, Danny Fenton, are caught off-guard when Danny's birthday party is moved up a week, as Danny, his mother and father and infant sister Danielle are preparing to move the following week. The toys' leader and Danny's favorite toy, an old fashioned Mountain boy doll named Stan Marsh organizes the other toys, including Margo Gru, Courage the Cowardly Dog , Arlo the Dinosaur , Leonard the Piggy Bank and sparky the Slinky Dog , into a scouting mission. Green army men, led by Sarge , spy on the party and report the results to the others via baby monitors. The toys are relieved when the party appears to end with none of them having been replaced, but then Danny receives a surprise gift – an electronic toy Toon Ranger action figure named Dexter: Boy Genius , who believes that he is an actual Toon Ranger.
Dexter impresses the other toys with his various features, and Danny begins to favor him, making Stan feel left out. As Danny prepares for a family outing at Pizza Spaceport, his mother allows him to bring only one toy along. Fearing Danny will choose Dexter, Stan attempts to trap him behind a desk, but ends up knocking him out a window instead, resulting in the other toys accusing Stan of murdering Dexter out of jealousy. Before they can exact punishment, Danny takes Stan instead and leaves for Pizza Planet. When the family stops for gas, Stan finds that Dexter has hitched a ride on the car as well, and the two fight, only to find the family has left without them. They manage to make their way to the restaurant by stowing away on a pizza delivery truck, where Dexter, still believing he is a real Toon Ranger despite Stan's attempts to convince him otherwise, gets himself stuck in a crane game, where he is picked out by Danny's destructive neighbor Beavis .
Dexter attempts to escape from Beavis's house, but fails, and, finally discovering the hard way he is a toy, sinks into despondence. Beavis plans to launch Dexter on a firework rocket, but his plans are delayed by a thunderstorm. Stan tells Dexter about the joy he can bring to Danny as a toy, restoring his confidence. The next morning, Stan and Beavis's mutant toy creations rescue Dexter just as Beavis is about to launch the rocket and scare Beavis into no longer abusing toys by coming to life in front of him. Stan and Dexter then leave Beavis's house just as Danny and his family drive away toward their new home.
The duo try to make it to the moving truck, but Beavis's dogs, The Greaser Dogs, see them and gives chase. Stan tries rescuing Dexter with Danny's RC car, but the other toys, thinking Stan eliminated RC as well, attack and toss him off the truck. Having evaded the Greaser Dogs, Dexter and RC pick up Stan and continue after the truck. Upon seeing Stan and Dexter together on RC, the other toys realize their mistake and try to help them get back aboard but RC's batteries become depleted, stranding them. Stan ignites the rocket on Dexter's back and manages to throw RC into the truck before they soar into the air. Dexter opens his wings to free himself from the rocket before it explodes, gliding with Stan to land safely into a box in the van, right next to Danny.
On Christmas Day, at their new house, Stan and Dexter stage another reconnaissance mission to prepare for the new toy arrivals. As Stan jokingly asks what might be worse than Dexter, they discover Danny's new gift is a puppy, and the two share a worried smile.
Since that day, they've been the best of friends, but what could be more strong than friendship? Perhaps the idea of immortality?