When reports of a creature stalking the seas nearby a tiny coastal town begin to surface, a young woman named Gutiere investigates. What she finds is not monster at all, but an "amphibian man," who must live in the sea. The beautiful Gutiere is charmed, and quickly falls in love with her new-found friend, but her fiance Zurita poses a distinct threat to both of their lives. This Soviet-era Russian sci-fi film is based on an original novel by popular science fiction novelist Alexander Belyaev.