New Moon is the name of the ship crossing the Caspian Sea. A young Lt. Petroff meets the Princess Tanya and they have a ship board romance. Upon arriving at the port of Krasnov, Petroff learns that Tanya is engaged to the old Governor Brusiloff. Petroff, disillusioned, crashes the ball to talk with Tanya. Found by Brusiloff, they invent a story about her lost bracelet. To reward him, and remove him, Brusiloff sends Petroff to the remote, and deadly, Fort Darvaz. Soon, the big battle against overwhelming odds will begin.