This episode opens with the Scarecrow explaining all about quicksand to Dorothy. Unfortunately, the topic comes up because the Cowardly Lion is trapped in some! This leads into a general discussion about just how smart the Scarecrow is. Back in the Emerald City, Ozma declares a friendship parade, celebrating the friendship between the Emerald City and Munchkinland. She declares that the venue will be the Yellow Brick Bridge joining the two together. Then Scarecrow points out that there isn't a Yellow Brick Bridge! Since this won't do at all, Ozma puts the Scarecrow in charge of constructing a bridge before he can explain that he doesn't actually know how to build a bridge! Wanting to save face and not letting everyone down, the Scarecrow bluffs his way through things. After several false starts and a few hijinks, they eventually put up a rickety bridge-like structure—that Dorothy, Tin Woodman, and Lion fall through, getting swept down the river! In his attempt to rescue them, the Scarecrow knocks himself out, and the rest must have saved themselves somehow because he wakes up to their concerned faces. The Scarecrow admits he doesn't know how to build a bridge, and Dorothy explains that that's okay, nobody can know everything, because then there'd be nothing left to learn. The gang all pitch in to rebuild the bridge, which looks a lot stronger, and it is dedicated by Ozma and the Munchkin mayor. All's well that ends well, but the Scarecrow seems to have had enough of bridge building.
This is probably not this show's finest hour, as there is a lot of acting out of character. I would have thought the Tin Woodman and the Lion, at least, would have observed the Scarecrow's difficulty and asked if he knew what he was doing. This version of Ozma is a bit of a steamroller, which isn't out of character. And Dorothy's understanding and positive can-do-it-iveness once she finds out totally fits. And I did have a little insider knowledge grin when the Lion mentioned making other bridges to Winkie Country, Gillikin Country, and Quadling Country.
One last thought: Hey, Ozma, do you have no construction crews or architects or anyone else in the country who can do anything? Why do Dorothy and her friends have to do it all?