The play begins on March 18, 1918. In the dugout officers' quarters of the British trenches, less than a hundred yards from the German trenches, Hardy dries his sock over a candle flame before he hands off duties to C Company's Osborne. The two talk about an impending major German offensive attack. Hardy goes over vital information, maps and logistical details, and some situational report topics. They joke about the miserable conditions and poor-quality rations. Hardy then gossips about Captain Stanhope, Osborne's superior and the Commanding Officer of C Company. He speaks negatively of Stanhope's heavy drinking, his youth, and his mercurial temperament. He suggests that Osborne should command C Company. Osborne rejects the notion and defends Stanhope, whom he says he loves. Hardy leaves.
Raleigh, an 18-year-old officer, reports for the first time to Osborne. Raleigh reveals that he wanted to join the company because his sister is engaged to Stanhope. Osborne detects Raleigh's idolization of Stanhope and gently cautions him that life on the front lines has a habit of changing men.
Stanhope and Trotter enter. Stanhope is dazed at the sight of Raleigh. After dinner, Stanhope has Raleigh join Trotter on duty to get him fully acquainted. Hibbert comes off watch duty and enters, complaining of neuralgia pains. He refuses dinner and turns in to bed early. Stanhope tells Osborne that he doesn't believe Hibbert is ill and they talk about Raleigh's connection to, and hero-worshipping of, Stanhope, as well as his relationship with Raleigh's sister. Stanhope is not pleased and tells Osborne he'll censor any letters Raleigh writes; he would like Raleigh's sister to continue thinking he is a war hero, and wishes to conceal any information related to his constant drinking. Osborne tucks an exhausted and angry Stanhope into bed.
The front lines are quieter than usual. Word comes down from the Colonel to Stanhope that a major attack is planned for dawn in two days' time. Stanhope orders preparations to hold their ground, wishing to line the sides of their position with barbed wire so that the platoon cannot run away but must hold position and fight.
In the lead up to the attack, the Colonel returns and tells Stanhope to immediately plan a raid across no man's land to capture a German soldier. Osborne and Raleigh are chosen to lead the capture raid, though Stanhope is reluctant to carry it out given the likelihood that they will suffer casualties. The raid is successful in that Raleigh captures a young German soldier who is immediately questioned by the Colonel; however, Osborne dies by grenade during the raid. The news leaves Stanhope grief-stricken and Raleigh shell-shocked.
Before dawn the day of the attack, the men prepare and take their positions on the line. Stanhope stays in the dugout making his own final preparations as he listens to the sound of bombs and gunfire growing louder and closer. The Sergeant-Major reports to Stanhope that Raleigh has been paralyzed by a shell fragment that broke his spine. Stanhope orders that Raleigh be brought to him immediately. Raleigh wakes up on Osborne's old bed with only Stanhope in the room. They speak for a while, addressing each other by their first names. Raleigh asks for a candle to be able to see in the dark, and by the time Stanhope returns with it, Raleigh has died. The Sergeant-Major comes in with a dire message from Trotter, asking for Stanhope. Stanhope walks stiffly out of the dugout, leaving Raleigh alone. A shell falls on the roof and snuffs out the candle flame. The sandbags and wooden beams holding up the entrance fall in, entombing Raleigh's body. The play ends with the muffled sound of intensifying warfare outside.