1917 On 6 April 1917, aerial reconnaissance has found that the German army is retreating from a sector of the Western Front in northern France, is not in retreat but has taken a strategic withdrawal to the new Hindenburg Line, where they are preparing to overwhelm the British with artillery. Within the British trenches, which have the telephone lines in the field cut and two young British lance corporals, William Schofield, a veteran of the Somme and Tom Blake, are ordered by General Erinmore to deliver a message to Colonel Mackenzie of the 2nd Battalion of the Devonshire Regiment, calling off an attack scheduled for the following morning, which could endanger the lives of 1,600 men, including Blake’s brother Joseph, who is a lieutenant.
Schofield and Blake Schofield and Blake crossed into the wilderness to get to the abandoned German trenches. Schofield was injured while on his way. Inside an underground barracks, they spot a tripwire that was set by the Germans that is ignited by an escaped rat; the explosion almost kills Schofield however Blake is able to save him and the two escape. They find themselves in an abandoned farm, where there is a German plane is shot down in an dogfight against Allied aircraft. Schofield and Blake are able to rescue the pilot from the wreck. Blake persuades Schofield to bring water to the pilot. After Schofield’s back is turned the pilot stabs Blake. Schofield shoots the pilot to death and offers comfort to Blake while he is dying and promises to complete the mission and to write to Blake’s mother. A passing British unit picks up Blake’s rings dog tags and Erinmore’s note.
Schofield accepts to release of the British lorries that are unable to cross the damaged canal bridge at Ecoust-Saint-Mein. He makes use of what remains of the bridge to travel without assistance, and is then subject to fire from a shooter. Schofield and the sniper exchange shots and Schofield shoots back. The sniper is killed while Schofield is hit in the helmet and knocked unconscious. He wakes up at midnight and strolls through the flame illuminated ruins of the town. After escaping from the attention of a German soldier, he finds a French woman hiding with an infant. She helps him heal his wounds and he offers her can of food and milk that he collected from his farm. Despite her appeals, Schofield leaves, after hearing the sound of a nearby clock and realising that time is running out. After spotting German soldiers, he strangles one to death and is able to escape by leaping into the river. The river carries him while the cherry blossoms are falling. Before reaching the riverbank, he is swept across an abyss. Within the forest, he spots D Company of the 2nd Devons, which is in the final wave of the attack. Schofield attempts to get in touch with Colonel Mackenzie while the unit advances towards the front.
Schofield realises that the trenches are too full for him to get to Mackenzie in the time he requires. He races across the open field parallel to the British trench lines just as the infantry starts its assault. He makes his way to meet Mackenzie who is able to read the message and then reluctantly decides to call off the assault. Schofield looks for Blake’s brother and finds him, who was part of the first wave and is bleeding but not injured. Schofield communicates with Joseph of his mission as well as Tom’s passing. He also shares Tom’s rings, as well as the dog’s collar. Schofield is deeply concerned about Joseph’s brother, but Schofield is grateful to him for his efforts. Schofield requests permission to write to Joseph about his brother’s bravery. Joseph accepts. Schofield exhausted, he lies down beneath an adjacent tree to gaze at photos of his family and wife.