If you keep in mind that you are reading a 4th-5th grade level book, this series is enjoyable. My 12 year old son finished them all quickly and enjoyed the puzzles and the cards. I like the fact that there are so many historical facts and international locations involved. Kids who may not normally be interested in history are told in a fun & exciting way about the past and are learning without even realizing it. This 2nd book in particular focuses on Mozart after the Cahill's found a link from Ben Franklin to him in the 1st book. Much about Mozart's life, his music, where he lived, ect. is discussed in this book, but never in a dry, over-informative way that would turn off kids. They also visit several European cities and learn a little about them along the way. This book isn't wonderfully written, but it keeps kids interested. I do wonder where all these clues are leading and if 10 books is worth it. There are too many close-calls for a 11 & 14 year old to reasonably get out of, but then again it is a kids book. Overall, there is no questionable behavior (other than some emergency theivery), language, or themes, but there is history, adventure, and critical thinking. Much better than many other books or the video games your kids could be playing instead.