The moon Ilmatar lies on the edge of the known universe. It is gripped by a blanket of ever-cracking ice and the freezing depths of the ocean. A scientific expedition at the Hitode submarine station explores these wonderful life forms as well as the ancient local culture. But in the name of civilization, other visitors come from space.
 
 The sea under the ice unexpectedly becomes the scene of an impending intergalactic conflict between humans and a hostile alien species. However, it does not belong to any of them, it belongs to the Ilmatars.
 It's their sea.