Years later Rolo is home alone, bored, now 44, chubby and balding. Zira comes home with her sulky teen sister Riffa, who refuses to play with her, and they argue. They take Rolo to the vet then the earthling park, along with his pet animal Quiggles. Rolo sees protestors for earthling rights, which sparks his curiosity. He asks Zira where earthlings come from, but that information is mysteriously missing.

At the park, Rolo tells his friends he wants more in life than just being a pet. Two Animal Control bots try to catch Rolo for being unlicensed, but his friends help him escape into the subway, which is actually a network of wormholes around the planet. He runs from the bots, Zira, and Riffa, but gets lost in a strange city with no way back, along with Quiggles and his friend Smuffins.

Rolo persuades Smuffins to help him find out where earthlings come from before they go home. They go to a pet store to ask, but all they learn is that earthlings are “alien” to planet Blorx. Nearby, Zira and Riffa are looking for him. When they see him, he runs and hides in a warehouse. Then Rolo is nearly attacked by monster rodents, but a mysterious man rescues him, a street earthling named Zeffro. Rolo is amazed by Zeffro’s independence.

Animal Control almost finds Rolo, but Smuffins draws them away, allowing himself to get caught. Rolo goes to a museum to learn more about earthling origins, but he can’t get in. Zira and Riffa see him again, so he tricks Zira into getting them into the museum. There they run and play, but the old curator Madame Zananna pulls them into her office. She senses Riffa’s tension toward Zira. She takes a liking to Rolo so she tells them about the fabled planet Earth, but to learn more she says they need to find Capt. Blarzenhook.

As they leave the museum and hide from Animal Control, Riffa gets angry when she sees their brother’s model rocket in Zira’s backpack. Zira explains she took the model as a memento of their brother who was abducted by other aliens. Later, Rolo tricks Zira to go in the tavern to find Capt. Blarzenhook. There the captain tells the myth of how aliens were part of Earth history and they abducted earthlings as pets, and a clue to Earth’s location.

As they leave the tavern, Rolo realizes he wants to go find Earth. Zira refuses to let him go, they get in an emotional argument, and he runs away. Zira cries because she’s all alone: Rolo ran away, her brother is gone, and Riffa is mean and aloof. Riffa is surprised to learn this, and she tries to comfort Zira. Meanwhile Rolo realizes he foolishly has no plan and nowhere to go, so he reluctantly rejoins them.

All along, Animal Control bots have been monitoring their movements from their high-tech military command center, and their forces closing in.

On their way home, they pass by a boardwalk amusement park, where Zira has memories of their sisterly bond when they were younger, which touches Riffa. Zira runs into the arcade and sings karaoke; Riffa joins her in duet as they sing about their bond.

Then the two Animal Control bots crash in and chase them around the boardwalk, and Riffa saves Zira’s life. They escape into the subway and return to the earthling park, but five huge Animal Control bots are there waiting and capture Rolo and Zira. Rolo’s friends come fight the bots using their pet toys.

Zira, Riffa, Rolo, and Quiggles escape to the forest, safe from the bots. Riffa urges Zira to think about what Rolo really wants, so Zira leads them to the hilltop. She hands Rolo her brother’s model rocket and says he can use it to find Earth. The model expands to a full size rocket. They say goodbye, and Rolo and Quiggles take off into the night sky.

Over time we see Zira and Riffa having fun together. Rolo and Quiggles have fun on their “road trip” and finally find Earth.