There are very few books that begin with the letter "X" (minus the words "a," "an," and "the"). Needless to say, I picked what I thought was a book that looked somewhat interesting. I was wrong. This was surprising because Lloyd Alexander is a Newbery Medal winner, so I expected a more engaging story.
Basically, the main character (Vesper Holly) and her friends are excited to be sailing off to the newly-discovered archaeological site of Troy. Before they reach Troy, she and her friends are tricked and imprisoned in a palace called Xanadu.
Xanadu's master is Dr. Helvitius - Vesper's arch-enemy. His goal is to dominate the world, and the first step to doing that is destroying Vesper. She has thwarted him often, and each time he ramps up his efforts to get rid of her.
Perhaps part of the challenge in reaching this book is that these characters have been introduced in other books, so this one builds upon other experiences that they have had. Reading The Xanadu Adventure was liking walking into an event where everyone knew what was going on - except for one person. In this case, the reader who had not read any books with Vesper Holly in them.
I ended up skimming most of the book and then giving up towards the end. I just could not identify or be interested in the characters or plot line. It was better to end the book prematurely than dragging out something that was miserable to read. There were other things that were deserving of my time.