The Very Detective Rattuses

I know I've said repeatedly that I'll never write a series, but that's when it comes to grown-up books. With children's books, the rules are out the window! As indeed are The Little Rattuses, which is how they escaped from the airplane that was taking them to a lab. Now they live on a farm and have fun adventures every day. This time out, they become detectives! Who is leaving strange alphabet letters around the farm?! What do the letters mean? Can The Little Rattuses solve the mystery? Can you figure it out before they do? And will they ever escape the dreaded Xylophone?