Kathryn R. recommends The Wall in the Middle of the Book by Jon Agee

Things are not what they seem in this cute story about a knight and an ogre. Which side of the wall is the safest--the one with the ogre or the seemingly safe "clear" side of the moat? Read it to find out!
Publisher description:
A knight who feels secure on his side of the wall that divides his book discovers that his side is not as safe as he thought, and the other side is not as threatening.