Castles in the Sky

Castles in the Sky is the first episode of Season 9, which aired on December 27, 2004.

Plot
There is snow on the ground and Arthur and Buster decide to have a race to the treehouse. When they arrive at the treehouse Arthur loses the race, but the treehouse collapses under the weight of all the snow. The rest of the gang soon meet at the Sugar Bowl discussing the first day the treehouse was built and they then meet Frank Gehry. Soon the gang began disigning a new treehouse and when they introduced the ideas to Frank at the Sugar Bowl, but in the end the gang decided that instead of a different design the orginal one was much better. So the treehouse is rebuilt the way it was before and Frank leaves giving them a picture of a building he designed and it's only then everyone realizes who he really is.