When sixth-grader Lily Grabowski takes in her teacher's puppy-mill rescue dog, without parental permission, it sets off a chain of events that challenges her dog smarts, self-esteem, and ideas about what it means to be a true friend.

As Lily's heart opens to this tiny dog, complications mount. Cagney howls all day because of separation anxiety. Lily's nemesis neighbor threatens to call the dog warden about a noise nuisance. BFF drama threatens Lily's class project on why underdogs matter. Lily's over-protective mom issues a thirty-day ultimatum, and Lily's guilty conscience grows while a broken promise looms.

In the end, Lily must choose. Either surrender Cagney because his needs are bigger than her ability to help him or stand up for what she believes will save him.