Even if you haven't read the first book, Lady Ellen provides enough back story to get you up to speed quickly. (Though I recommend Book 1 for an equally good read!) If you're looking for a quick, easy read that is both thrilling as well as funny, I highly recommend The Cauldron of Ceridwen.
I also appreciated the terrific characterization of secondary characters, including P-C and Benson who are endearing and sometimes laugh out loud funny. Enjoy.