Hiding, lying in wait on the sea bed, is EX16, one of the most important ships in the Royal Navy. She’s not much to look at, and she’s only 54 feet long, with no defensive armament. But her four-man crew knows that the outcome of the war could depend on this midget submarine. Seaton, her commander, understands what his men face. There is the boredom, the discomfort, the jealousy and bickering; and already they have confronted enormous dangers on desperate raids into Norway. Now, poised for the attack on a secret Nazi rocket installation, Seaton must hold his crew together for the hell that awaits them.