Rex is an unusual kind of guy.  He is funny.  He is smart and yes, he is in sixth grade. At any rate, in this new entry to what we hope is going to be a long series, Rex and friends decide to replace their substitute teacher. There is mystery and fun and laughter in this book. It is like Hank Zipper and Joey Pigza meet Miss Nelson is Missing.  It all adds up to much more than zero.