Russel Wright finds a portal under his bed leading to an alternate universe called Under. Since he is from Up and acquires the crown of Under, he is proclaimed the King.
In order to make ice cream, Vernon and Loopy set up a factory with a blizzard inside it, causing the outside world to turn into a desert. When Russel decides to get rid of the ice cream in favor of the climate, Bob starts a coup. Meanwhile, Near Under is beset by the petrifying Hairy Eye-Ball, so Auntie and Russel make a deal to solve each other's problems.
Gus digs up a dinosaur bone in Up but when he takes it down to Under, Vernon's latest gizmo reanimates it. Gus feels Russel loves the dinosaur more than Russel does Gus, so Loopy takes him to find the Everything Log so he could wish it away. But, Auntie had already gone missing looking for it, and Bob decides to try to find it himself too.