Summer, 1914: At a Berlin opera house the performance is disrupted by the announcement of war. The life and career of the singers Anna Sørensen and Nikolaus Sprink changes, as Nikolaus has to go to war. In Scotland, William urges his younger brother Jonathan to enlist. In Paris, pregnant Madeleine is angry as her husband Audebert departs for war.
December 23, 1914: An attack by French and Scottish soldiers on the German line fails. Nikolaus stabs a man and despairs at the violence. William is shot and dies. In the bunker later, the soldiers are shocked by the slaughter.
December 24, 1914: In the morning, little Christmas trees are delivered to the German soldiers, a gift of the Kronprinz who is camping in a chalet nearby. Nikolaus is ordered to sing for him later and looks forward to reunite with Anna at that occasion. The French soldiers receive wine, sausages, and chocolates. The Scottish soldiers get crates of whiskey. Later, in the evening, Anna and Nikolaus perform for the Kronprinz. Nikolaus has to return to the front, and Anna follows him. At night, a French soldier moves out with some grenades to infiltrate the German line. Some Scottish soldiers start singing. Nikolaus responds with a Christmas song ("Silent Night"), soon the Scottish bagpiper starts to accompany him, and Nikolaus raises a Christmas tree on the bunker. The Christmas truce starts as the lieutenants agree to stop fighting until the morning. The soldiers come out and the French soldier returns without using his grenades. The soldiers intermingle, talk, and exchange provisions. Anna appears. Father Palmer conducts a mass. Anna sings of peace. Jonathan, however, finds the body of his brother and vows to take revenge.
December 25, 1914: In the morning Jonathan buries his brother. A decision is made to extend the truce to allow for the burial of other soldiers. Later in the morning Father Palmer delivers the last rites as the bodies are carried away. During the day, the news of the truce reaches the British, French, and German headquarters. It is received with disbelief, anger, and the determination to punish the soldiers. In the evening Horstmayer wants to arrest Nikolaus for insubordination, but Anna takes his hand and leads him across the no-man's land toward the French side. Horstmayer's order to shoot him is ignored. Nikolaus and Anna ask the French for asylum.
December 26, 1914: The British Major punishes the Scottish soldiers by transferring them to the front lines. On his order, Jonathan shoots a German soldier crossing the battlefield. The soldier is actually the Frenchman, Ponchel, in a German uniform who was disguised to cross the lines and visit his mother. The French General orders Audebert to Verdun and disbands his unit. The Kronprinz transfers the German soldiers to Pomerania. The no-man's land is empty at the end.