At the height of the First World War, two young British soldiers must cross enemy territory and deliver a message that will stop a deadly attack on hundreds of soldiers.
| Lance Corporal Schofield | George MacKay |
| Lance Corporal Blake | Dean-Charles Chapman |
| Captain Smith | Mark Strong |
| Lieutenant Leslie | Andrew Scott |
| Lieutenant Blake | Richard Madden |
| Lauri | Claire Duburcq |
| General Erinmore | Colin Firth |
| Colonel MacKenzie | Benedict Cumberbatch |
| Sergeant Sanders | Daniel Mays |
| Major Hepburn | Adrian Scarborough |
| Private Bullen | Chris Walley |
| Sepoy Jondalar | Nabhaan Rizwan |
| Lieutenant Richards | Jamie Parker |
| Private Butler | Tommy French |
| NCO Baker | Paul Tinto |
| NCO Harvey | Billy Postlethwaite |
| Colonel Collins | Richard McCabe |
| Captain Ivins | Justin Edwards |
| Lieutenant Gordon | Pip Carter |
| Sergeant Miller | Andy Apollo |
| Private Stokes | Josef Davies |
| Private Buchanan | Gabriel Akuwudike |
| Private Kilgour | Spike Leighton |
| German Pilot | Robert Maaser |
| Private Parry | Gerran Howell |
| Private Atkins | Adam Hugill |
| Sergeant Harrop | Benjamin Adams |
| Private Cooke | Anson Boon |
| Private Rossi | Kenny Fullwood |
| Private Malky | Ryan Nolan |
| Private Sniper | Elliot Baxter |
| German Soldier | Kye Mckee |
| French Baby | Ivy-I Macnamara |
| Soldat Muller | Merlin Leonhardt |
| Soldat Baumer | Taddeo Kufus |
| Wayfaring Stranger Soldier | Jos Slovick |
| Private Pinwood | Luke Hornsby |
| Private Seymour | Jack Shalloo |
| Private Grey | Elliot Edusah |
| Lance Corporal Duff | Jacob James Beswick |
| Lieutenant Hutton | Michael Jibson |
| Sergeant Wright | Ian Wilson |
| Sergeant Gardner | Bradley Connor |
| Sergeant Guthrie | John Hollingworth |
| Orderly Dixon | Michael Smith |
| Orderly Byrne | Jonny Lavelle |
| Captain Rylands | Michael Rouse |
| Mackenzie Officer | Richard Dempsey |
| Mackenzie Officer | Phil Cheadle |
| Captain Morahan | Jonah Russell |
| Captain Sandbach | Daniel Attwell |
| Private Willock (as Joe Mendes) | Joe Anders |
| German Sniper | Bogdan Kumšackij |
| Attacking Soldier (uncredited) | Oliver Simms |
