It is late summer, 1914 and the great powers of Europe, divided into two coalitions, have declared war on each other.
In Berlin, the declaration of war interrupts two opera singers; Anna Sørensen and Nikolaus Sprink, as they perform on stage. In Scotland, William Dale convinces his younger brother Jonathan to enlist. In Paris, Madeleine Audebert, pregnant with her first child, argues with her husband as he prepares to depart for the war.
It is two days until Christmas. On the battlefields of Belgium, the conflict rages. William Dale is shot down in no-man’s land and his brother Jonathan is forced to abandon him. In the German bunker, Nikolaus receives an order to sing at the nearby chalet of the Kronprinz on Christmas eve.
The next day, upon returning, Nikolaus hears the Scottish soldiers singing from across the battlefield and responds with a rousing Christmas song. The Scottish join in and emboldened by this, Nikolaus stands atop the bunker with a Christmas tree held up as a gesture of friendship. The lieutenants of each side cautiously meet in the middle of the battlefield and agree to a truce for the rest of Christmas eve. Jonathan buries his brother and vows revenge.
News of the cease-fire reaches the commanding officers of the French, German and Scottish troops, who all decide to punish their insubordinate soldiers.
Lieutenant Audebert learns that his wife has given birth to a son and vows to survive the war as he is relocated to Verdun. Nikolaus and Anna decide to flee together and bravely cross the no-man’s land to demand asylum in France, whilst the remaining soldiers are each reassigned to other battlefields as punishment for the truce.
As the German soldiers depart the battlefield, they hum the Scottish ballad they heard in the bunker on Christmas Eve.