This world was... In it, humanity did not go “up” into the atmosphere and space, but descended into the depths of the World Ocean. Airships hovered in the skies, and giant submarines transported people to underwater cities and shelf platforms. Now he is gone. From the unknown universe, having tamed matter and space, came ruthless, invincible enemies under black and white flags with a three-pointed swastika. A war has begun in which surrender is not accepted and there is nowhere to run. But one cannot win without assessing the strength and weakness of the enemy legions. And while their compatriots are preparing for new battles, scouts on a submarine go to an alien world to study the enemy. Where victorious evil triumphs, only duty and courage will become their protection and support.