After a mysterious explosion leaves a large fissure in the ground, two young boys are confronted by an unknown phenomenon that inflicts severe radiation burns on one of them. There follows a spate of attacks at radiation establishments as the inexplicable life-form plunders radium stores. Dr Royston, an expert in atomic research, is brought in to explain and curtail the activities of this alien creature before it causes disaster.
A British Corporal in France finds himself responsible for the lives of his men when their officer is killed. He has to get them back to Britain somehow. Meanwhile, British civilians are being dragged into the war with Operation Dynamo, the scheme to get the French and British forces back from the Dunkirk beaches. Some come forward to help, others were less willing.