"Soul music sets the stage as Caveman Austin leads a prehistoric chase through Rockville to catch his runaway dinosaur puppy. But can anything stop a runaway dinosaur?"
Austin is shown in the backyard. He explains to the viewer how he is living in prehistoric times as a caveman, and is so excited about going to the pet store and getting a pet. He sings the song "I Want a Pet". Austin then ventures into the stone-age town of Rockville, which the backyard transforms into suddenly.
Austin is riding on a skateboard through the town to get to the local pet store, "Pet-a-Store-us". His skateboard runs into a tar puddle and is stuck in the gooey mess. Austin frequently tugs at his board, struggling to move it. The skateboard flings out of his reach, twirls in the air, and lands in front of Austin. He rides it to the pet store.
Uniqua, the store owner, is standing outside of Pet-a-Store-us. Austin gets off his skateboard to talk to the employee. Austin gives Uniqua five pebbles, used as money. He explains to the owner how he wants a pet that like to play fetch, go to the park, and is really energetic. Uniqua knows the type of pet he wants - a dinosaur puppy. Austin spies a playful, long-necked dinosaur in the store window and asks if he could have it.
Uniqua agrees, and lets the dinosaur out of the store. She gives Austin a leash. He holds on to it as the dinosaur runs off carrying Austin behind. Uniqua yells to Austin not to take off the leash, but Austin misunderstands her words because he was too far away to hear her. The dinosaur, named Boy during the ride, takes Austin to the park. As they arrive at the park, Austin plays with Boy while singing the song "I Got a Pet". He takes off his leash. Boy immediately runs away. Austin tries to yell after him, but Boy does not come back. He chases Boy a bit deeper into the park, but it is no use.
Austin dashes back to Pet-a-Store-us to ask Uniqua for help. Austin tells Uniqua how Boy ran away when he took off the leash. Uniqua tells him that she had previously told him to never take off the leash, and now the only way to get Boy back is to whistle for him. Austin now understands what she had said, but doesn't know how to whistle. They both sing the song "I Need a Hand". Uniqua gives Austin a ride on her motorcycle. They drive to the park to look for Boy.
On the way, they spot Boy. Uniqua creeps up to him and gives him a bone to distract him and allow her to put the leash back on, but ends up holding on to Boy's tail, being pulled away in the air by him. Austin knows he should help Uniqua, so he jumps on to the motorcycle to chase after his pet. While chasing him, Police Officer Pablo, in his police car, notices that Austin is speeding. He gets up, puts his glasses on, and chases after Austin, Uniqua, and Boy.
Austin looks behind himself and sees the giant car behind him. He tells Uniqua that they are part of a high-speed chase. Boy jumps over a tar puddle, making Uniqua fly in the air. She falls to the ground and lands perfectly on the motorcycle with Austin. Uniqua greets him, and she greets him back. Because of not paying attention to the road ahead, the motorcycle gets stuck in the tar puddle Boy previously jumped over. Pablo manages to catch up with them, and asks the two if they know why he was chasing them.
Austin answers "to say hi?" Pablo is tricked and says hello. However, he quickly gets back on track and tells them the real reason: Austin was driving too fast and Uniqua was riding around on a dinosaur. Uniqua and Austin apologize and tell Pablo that all they were doing is trying to get Austin's pet back. Austin spots Boy digging a hole to bury the bone given to him earlier. Pablo tells the two not to worry, because he has it all under control. He pulls out a megaphone and tells Boy to put the bone down and move away from the hole. Boy cannot understand his words and keeps digging. Pablo tells Uniqua and Austin that Boy is not listening. Austin asks Pablo if he can whistle. Pablo answers "no". He does show that he can tap his head and rub his belly.
Pablo gets a long grappling hook attached to his car bumper and hooks it on to Boy's collar. He thinks that if Boy is tied to his car, they can easily get a leash on him. But Boy runs off and breaks the bumper off of the police car. Pablo makes a note to himself to get a new car bumper. Uniqua gets on to her motorcycle, Austin gets on to his skateboard, and Pablo gets into his car as they all prepare to chase the dinosaur. They sing the song "Where Has My Dinosaur Gone?" while chasing Boy. Boy runs up a tree. Now the three can't think of a way to get Boy down. Pablo thinks for a while and knows what to do - call Fireman Tyrone. His firetruck has a tall ladder, which they could use to get Boy down.
Tyrone arrives and climbs up his truck's ladder and tries to get Boy down. But Tyrone tries so hard to get a leash on Austin's pet, he loses his balance and falls. Austin asks him if he can whistle, but Tyrone answers "no". Tyrone does show him that he can wiggle his ears. Boy runs down the tree and escapes. Now all four are chasing Boy in their prehistoric vehicles. Boy crosses a tar pit, and all of the Backyardigans' vehicles sink into the tar. The top of Tyrone's firetruck is still visible at the surface, and Pablo, Uniqua, Austin, and Tyrone gather on to the truck's top and sing "Now Would Be a Good Time to Whistle".
They all leap out of the tar pit as the firetruck sinks. Austin tries to whistle and finally succeeds. Boy comes over to Austin and allows him to put the leash back on. Tyrone's stomach grumbles. Pablo asks if the sound was another runaway dinosaur. Tyrone tells him that it is just his stomach, and invites everyone to his house for strawberries and yogurt. They all run to Tyrone's house as the prehistoric town turns back into the backyard. They all sing the end song and run into Tyrone's house. Austin whistles as the episode ends.