When wealthy crime novelist Harlan Thrombey (Christopher Plummer), the patriarch of an eccentric, combative family, dies following a family gathering to celebrate his 85th birthday, it’s at first believed to be a suicide. However, famed Southern detective Benoit Blanc (Daniel Craig) suspects foul play. He joins forces with a member of the local police, Detective Lieutenant Elliott (LaKeith Stanfield), to investigate.

Detective Blanc asks the family members to remain at the home until the investigation is completed. However, his request is met with disbelief, anger and contempt as the family members turn on each other.

At the height of the First World War, two young British soldiers, Lance Corporal Schofield (George MacKay) and Lance Corporal Blake (Dean-Charles Chapman), are stuck with 1,600 other British soldiers in the trenches of the Hindenburg Line on April 6, 1917.

Their superior, General Erinmore (Colin Firth), assigns them a challenging and dangerous task — to personally deliver a letter to Colonel Mackenzie , commander of the 2nd battalion.

In a race against time, they must cross enemy territory and deliver a message that could potentially stop a deadly attack on hundreds of soldiers — one of them being Blake’s own brother.