'1917' Trailer: Soldiers Embark on Dangerous Mission in Sam Mendes' World War I Epic

Colin Firth tasks Dean-Charles Chapman and George MacKay to stop a deadly attack on soldiers in World War I.

From Sam Mendes, director of Skyfall, Spectre and American Beauty, comes 1917, which centers on two British soldiers, Schofield (Captain Fantastic’s George MacKay) and Blake (Game of Thrones' Dean-Charles Chapman), who are given a seemingly impossible mission to cross enemy territory and deliver a message to stop an attack on hundreds of soldiers.

In the trailer, released Thursday, Colin Firth stands in front of Schofield and Blake, addressing Blake in talking about his brother, who is part of a battalion of 1,600 soldiers unaware that they are in danger. Blake asks about his brother's safety: "Is he…?” Firth finishes the sentence: "...Alive. And with your help, I would like to keep it that way.”

As Firth tells both of the young men they must go into enemy territory to stop the attack, a series of clips shows the danger ahead, with the men being shot at and swimming through areas filled with corpses of soldiers along with injured individuals and explosives in battlefields.

The trailer ends with Firth telling the two soldiers: "If you fail, it will be a massacre. Good luck."

Mendes wrote the epic with Krysty Wilson-Cairns. The cast also includes Benedict Cumberbatch, Andrew Scott, Richard Madden, Mark Strong and Claire Duburcq.

The Universal Pictures film will hit theaters in limited release Dec. 25 before expanding wide Jan. 10. Watch the trailer above.