Antonia "Ant" MacPherson is a sixth-grader who is convinced that her real parents have, for whatever reason, left her with the MacPhersons, and will someday (soon!) come back for her. Ant is sandwiched between two perfect blonde feminine sisters and has a hard time getting her parents (the ones she lives with) to commend her for anything. Her chihuahua, Pistachio, is the reason behind most of Ant's lies - her parents don't want the dog, who is old and needs to see a vet.
I really enjoyed the book, but it seemed to be a little somber for a children's book, in that Ant's parents seem so uncaring and harsh toward their daughter. However, I can concede that this may be simply because it's written from Ant's point of view, and she sees her parents as uncaring and harsh.
Either way, I think it's worth reading. Also check out Al Capone Does My Shirts by the same author.