Antoine, a boy living in Northern France at the outbreak of World War II, takes on the challenge of defending the family home after his father is drafted and sent to the Maginot Line. With the aid of his accomplices, war veteran Grandpa and imaginary friend Napoleon, Antoine digs trenches and stands guard by an old cannon in the front yard. Tensions mount just as the Nazis break through the Maginot Line, and the invading troops pass in front of the family home.