Bill Rohan (Callum Turner) fulfills his National Service requirement by enlisting in the Army. He and his friend Percy Hapgood (Caleb Landry Jones) are promoted to sergeant and assigned to teach typing to new recruits. They wind up locking horns with their superior, Sergeant-Major Bradley (David Thewlis), a World War II veteran and stickler for rules. Bill is charged with subverting morale by telling his pupils some discouraging facts about The Korean War then raging. His case is thrown out when he demonstrates that everything he said had previously been printed in The Times. Percy is less fortunate after the two of them and mischievous orderly Redmond (Pat Shortt) concoct a plan to steal a mess clock given to the regiment by Queen Victoria.
Off the base Bill falls in love with the mysterious Ophelia (Tamsin Egerton) while Percy takes up with impish nurse Sophie (Aimee-Ffion Edwards). For varying reasons neither relationship quite works out, but Bills older sister Dawn (Vanessa Kirby) also enters the picture.
- I Will Wait for You: Dawn cares enough for Percy that she rushes to the station and promises to wait for him after his court martial.
- My Sister Is Off-Limits!: Percy intentionally provokes this in Bill who he's mad at for having sex with Sophie. Bill is upset initially but their friendship recovers while Percy and Dawn become a lasting couple.
- The Neidermeyer: Bradley is regarded in this way by much of the unit due to his rules-obsessed and punitive behavior. Deconstructed when its revealed that much of it is a result of shell-shock from his previous war experiences.
- The Ophelia: Yes, Ophelia does live up to her name. Her final break with Bill comes when shes hospitalized for a suicide attempt.
- The Peeping Tom: Bill and Percy peep into a nurses dormitory with one standing on the others shoulders for a better look in the window. The plan literally collapses when Sophie gives them more than they bargained for.
- Reasonable Authority Figure: Major Cross, the commanding officer played by Richard E. Grant, is a fair-minded man mostly concerned with keeping Bradleys stringent loopiness in check.
- The Tease: When Bill and Percy try peeping in her dormitorys window, Sophie responds by exposing one of her breasts right near the window, with amusing results.