Young Carl Fredricksen, a quiet bespectacled boy wearing an old pilot's cap and goggles, watches a film reel in a theatre depicting his hero Charles Muntz, a famous explorer. The reporter speaks of Muntz's various accomplishments and discoveries before commenting that he was recently dishonoured by scientists who believed his latest find, the large skeleton of a bird, was a hoax. Intent on proving them wrong, Muntz is seen boarding his zeppelin with his team of dogs and promises to return once he has brought back living proof of his find. After the show, Carl runs down the street with his balloon, named after Muntzs zeppelin The Spirit of Adventure. He passes an old, rundown house where he hears someone shout out Muntz's famous slogan: Adventure is out there!
Carl goes inside to investigate and meets a young, outgoing tomboy who shares his passion for exploration and admiration of Charles Muntz. Startled by her loud, boyish demeanour at first, Carl loses his balloon in the rafters. The girl, Ellie, helps him retrieve it, though Carl falls from a beam and breaks his arm. Ellie sneaks into his room that night and shows him her adventure book where she expresses a desire to one day move to the top of Paradise Falls in South America, showing him a picture that she 'ripped right out of a library book'. She makes him promise that they will go together someday before leaving. Carl and Ellie eventually getting married and move into the old house where they first met. Their marriage is blissful and they get jobs as a balloon salesman and zookeeper, respectively. They plan for they plan for a baby, painting the room in advance when they discover the horrific news that Ellie can't have children. Carl and Ellie put a piggy bank together, putting shrapnel and the odd notes in to save money to eventually travel to paradise falls. However, as the years pass they are forced to break into their savings for other obligations which are more important. They do this for many years to come. An elderly Carl realises that, despite living happily together, they never fulfilled their old promise to each other of living on Paradise falls.
Carl, being the gentlemen he is invites Ellie for a picnic and was going to surprise her with tickets to South America when she falls critically ill, with her health declining all the time. Carl decides that he will get her to their childhood dream even if it kills both of them. They had been travelling for a year, very slowly, pulling alone their home and possessions, with their age not slowing down. He figured he would have to sacrifice something but didn't know what. Would it be their health and well being or their long lost dream?