In the tradition of Peter and the Wolf (Prokofiev) and A Young Person's Guide to the Orchestra (Britten), it was written to introduce children to orchestral instruments and "classical" music. It is a picture book with an accompanying CD, however the word play and a lot of the humour would appeal to adults more than children. I heard part of the story a few weeks ago on In Tune, one of the few CBC Radio 2 programmes that I still listen to (don't get me started!), and was doubled over with laughter.
Maybe it is because I am an occasional musician and former orchestra member that it particularly appealed to me, though my instrument did not fare well. The flutes were busy doing bird imitations when the composer died, and they claimed to be much to wimpy and high-pitched for murder :-) Fortunately the piano (my true love) was not involved in the whole scenario!
I loved this book, and can see myself giving copies of it away as gifts in the future!