Eleven-year-old Cooper Callaghan knows how to have fun, especially while living in what he calls "the greatest neighborhood in the world." Summer days are filled with elaborate games, adventures and the occasional practical joke on his temperamental older sister, Penny. But when Castle Hills' favorite grandpa, Mr. Wilson, loses something dear to him and his wife, Cooper and his friends face a mission that may be impossible to complete. With only a handful of hours before Mrs. Wilson arrives home for the big July 4th celebration, Cooper must search every corner of the community, out-smart his sister and overcome his own pride to save the day.