As noted previously, after being forced to continue the series, Baum started to phone things in. This isn't to say that his books were bad. Far from it - the work he churned out was still inventive, fun, and just plain entertaining. That said, he certainly became the king of taking shortcuts.
While "Patchwork Girl" was built on the skeleton of "Wizard," and "Tik-Tok" was lifted from the stage version of "Ozma," "Scarecrow" was constructed from two different sources: the silent film of the same name released in 1914, and the material Baum had prepared for a third Trot book. The result is actually one of Baum's best books, though I'm possibly biased since Trot's my favorite character in the series.
The plot follows Trot and Cap'n Bill as they make their way to Oz after almost drowning off the coast of California. They're saved by the mermaids from "Sea Fairies" (continuity!) and eventually get to Mo (dragging another Baum book kicking and screaming into Oz canon). At Mo, they meet Button-Bright again (because why not), and ride a ridiculous giant bird to Oz.
What follows is a romantic farce as Trot and Company watch the drama unfold between a princess, the boy she loves, and the cruel King Krewl. Krewl has the princess's heart frozen so she won't love the poor gardener boy anymore, but then the Scarecrow drops in out of nowhere to give everyone a happy ending.
After all of this wackiness has ensued, Trot and Cap'n Bill decide to stay in Oz forever, presumably because they both hate Trot's poor widowed mother. Seriously, Trot, you're a horrible daughter.
Author: L. Frank Baum • Year: 1915 • Info:Tor Online