In 1940, after Nazi Germany invaded France, thousands of Allied soldiers withdrew in the Dunkirk maritime city. As the British perimeter decreases more and more, the soldiers await evacuation, finding themselves in a seemingly hopeless situation. Tommy is a young British soldier who is among the group that reaches the gunfire of German soldiers on the streets of Dunkirk. He is the only one in his group to manage to reach the British perimeter where British soldiers and allies are waiting to be evacuated from the beach.
He meets Gibson there, another young soldier who seems to bury a friend. After an air raid by the Germans, they give over a wounded man who was left to die and take him in haste to a ship evacuating the wounded. They are not allowed to climb that ship so they hide behind a pier in the hope that they can sneak aboard the next ship.
However, the ship is attacked as soon as it leaves the shore, and in the chaos that occurs, they manage to save another soldier named Alex. They still have an unsuccessful attempt to leave, this time the Germans prevent them from doing so with a submarine. Commander Bolton and Colonel Winnant discuss this situation and get assured by the Prime Minister that all 30,000 soldiers will be safely evacuated in the end and will not come to any understanding with the enemy.