Dawson and Major Sykes are sent to Eben Emael in Belgium, the strongest fort in the world, completely impregnable. That night, activity in the village wakes them, and they return to the fort and witness a group of German soldiers land on the roof in gliders to assault it. The main attack lasts 20 minutes, leaving Eben Emael crippled. And Dawson is disturbed - he has seen the Germans do what he thought impossible - blasting holes through solid 12 inch steel armour plating using some kind of new demolition charge.
Sykes realizes that new German secret weapon could have enormous implications for the allies, affecting everything from the design of tanks, armoured buildings, even battleships. The two men manage to get back inside the fort and retrieve one. On their escape, Sykes is wounded in the leg, but Dawson devises a plan and manages to get Sykes out on a stretcher, with the demolition charge slung underneath it.
But when they eventually manage to battle their way to the Belgian lines, Eddie Dawson will face an epic attempt to make it to Dunkirk, while the German fighters and bombers do their best to kill them all.