I've read thousands of books for kids in my life, and King of Shadows by Susan Cooper is certainly one of the best.
It's about a boy in a drama troupe rehearsing to produce a play by Shakespeare who is transported back to the past and actually meets Shakespeare himself. But there's a lot more to the plot than that.
Anyone who is interested in Shakespeare or history will enjoy this book.
Anyone interested in drama or the theater will enjoy this book.
Anyone who likes a book with an exciting plot, realistic characters, and excellent writing will enjoy it.
And anyone who enjoys all three will absolutely love it, as I do.
Now I'll have to read more books by Susan Cooper.