In the late summer of 1914, three teenage boys in Suffolk—Will, Freddie, and Lacey—are out playing a game of football when they discover their opponents intend to enlist the British Army in light of the outbreak of the First World War.

Though their father wishes them well, their sister Annie cries, and their mother (Kate Winslet) warns her sons that war is not a game, and that they will be killed.

The boys leave for France regardless, where they quickly encounter hardships of the trenches, witnessing artillery barrages, dogfights, and dying soldiers.

As the seasons change to winter, the boys hear German soldiers in the opposing trenches singing Christmas carols.

All of the soldiers peacefully step out to play football, exchange pleasantries, and conduct shared funerals for their dead.