What book reunites Dorothy with the humbug Wizard from "The Wonderful Wizard of Oz" (1900), and had one of the earliest film adaptations?
Nathaniel D. Mann:  He composed at least two songs with Baum, "Different Ways of Making Love" and "It Happens Ev'ry Day," and another with John Slavin, "She Didn't Really Mind the Thing at All," for "The Wizard of Oz" stage musical in 1902, and in 1908, composed the first original film score (27 cues) for "The Fairylogue and Radio-Plays", one of the earliest feature-length fiction films (and the earliest film adaptations of the novels "The Wonderful Wizard of Oz", "The Marvelous Land of Oz", "Ozma of Oz", "John Dough and the Cherub", and "Dorothy and the Wizard in Oz", presented by Baum himself), which debuted September 24, 1908. Dorothy and the Wizard in Oz:  It was published on June 18, 1908 and reunites Dorothy with the humbug Wizard from "The Wonderful Wizard of Oz" (1900).
Dorothy and the Wizard in Oz