Tom Buckingham (Sam Heughan) is a special agent for the British government and is actually off duty. Together with his girlfriend Sophie, he is on his way to Paris to propose to her. However, the romantic weekend ends before it has really begun, in the middle of the Eurotunnel. A group of armed agents hijacks their train and takes all the passengers hostage. Their leader, cold-blooded mercenary Grace Lewis (Ruby Rose), seeks revenge for the death of her father, whom the government eliminated as an accessory to a dirty deal. Only one man can prevent her from blowing up the tunnel and killing hundreds of innocent people: SAS Sergeant Tom Buckingham!