1943. In a heat great " underwater war " sailors from the torpedoed American submarine "Fish - sword" become captives onboard German submarine U-429 under command of "old salt" Herdt. Germans are rather pleased уловом, not suspecting, that with itself янки have brought invisible death - a virus of a meningitis. Not knowing about intentions of the enemy, captain Trevers and his(its) fighting friends wait for any opportunity to lift revolt. But when epidemic destroys the most part of German crew, it becomes clear, that in gloomy enemy waters where hunters and victims are invisible also each mistake can become fatal, captives and their supervisors will survive, only if will help each other. Not seeing other chances of rescue, Herdt offers Trevers's the risky transaction...