Agatha H. and the Voice of the Castle

This is an excellent book, and the reader is fantastic. However, the audiobook omits the “To be Continued in Agatha H. and the Siege of Mechanicsburg” chunk that comes after the cliffhanger, which is rather frustrating.

Also, this book ends on a cliffhanger, and Agatha H and the Siege of Mechanicsburg isn't out yet, so keep that under consideration - though considering that arc of the comics also ends on a cliffhanger, you may even want to wait until the 5th novel, and then binge on the three of them. That way you're on a good stopping place while you wait for “Agatha H. and the Master of Paris.” or whatever book 6 will be titled.