I just finished reading a book that I don't think you can get any more — at least not under the same name I read it under. I enjoyed Professor Wogglebug and the Frogman of Oz by Cynthia Hanson, however, even if it was a bit simple and straightforward. That is not always a problem with Oz books. It seems the powers of the Truth Pond are catching up to the Frogman, and he not only has to tell the truth (which has been off-putting at times), but he is also reverting to his true froggy nature. His good friend, Professor Wogglebug, tries to help him, and it turns out that a teenager from Ohio named Teresa is the key to breaking the Frogman's curse. Sure enough, once she is brought to Oz, Terry has information that will help. The three of them set off on an adventure, and…well, let's just say everything turns out all right in the end, which I'm sure is not a surprise. I liked the characterizations of both of the two main characters, and Terry also does well working through her issues.
As I said, this book appears to no longer be available. But it also appears to have been reissued under another title, Mr. Wogglebug, the Frogman, and Terry Volume 1: How the Truth Can Heal. I can't tell if all of the book I read is in this book or only part of it, but at least it looks like there will be more adventures with this trio of characters.