Carl Fredricksen (voice of EDWARD ASNER) always dreamed of traveling to South America, thanks to the adventures of legendary explorer Charles Muntz (voice of CHRISTOPHER PLUMMER) who traveled there in his zeppelin, "The Spirit of Adventure," in search of a prehistoric bird known as "The Monster of Paradise Falls."
Yet, Muntz never returned and Carl grew up to become a balloon salesman, happily married to his childhood sweetheart Ellie. Life, however, got in the way of their plans to visit Paradise Falls, and now that she's passed on and their house is the lone one left standing in their former neighborhood turned construction zone, Carl's become a 78-year-old curmudgeon.
Accordingly, he isn't happy to have 8-year-old Russell (voice of JORDAN NAGAI) knocking at his door. He's a Wilderness Explorer who needs his "assisting the elderly" badge to move up to the senior level, but Carl wants little to do with him.
Besides, he has bigger concerns, having whacked a construction worker for damaging his mailbox. With the court set to take his home away, Carl decides to take off -- literally -- via a massive array of helium balloons attached to his house. But he's unaware that Russell has become an unintentional stowaway, and after a rough thunderstorm encounter, they find themselves floating above South America.
With Carl's only desire being to put his house down at Paradise Falls, he and Russell become unlikely traveling companions, eventually joined by a large prehistoric bird that Russell names "Kevin." There's also Dug (voice of BOB PETERSON), a dog that can talk thanks to a technologically advanced collar and who was part of a pack led by Alpha (voice of BOB PETERSON), sent out by their master to capture "Kevin." From that point on, Carl and Russell try to walk their floating house to the falls, all while avoiding Alpha, the other dogs, and their master who believes the outsiders are after his prized bird.