People living at a seashore town are frightened by reports of an unknown creature called “the sea devil”. Nobody knows what it is, but it’s really the son of doctor Salvator. The doctor performed surgery on his son and now young Ichtiander can live under water. This gives him certain advantages, but also creates a lot of problems.

In 1919, Hungarian Communists aid the Bolsheviks’ defeat of Czarists, the Whites. Near the Volga, a monastery and a field hospital are held by one side and then the other.