Young Alena lives in a small seaside town. She is cheery, pretty, and kind - just like a fairy mermaid. That's why friends call her Undine. Alena works in dolphinarium where she got her unchangingly good humor and beautiful tan. Undine's life changes dramatically when family of a businessman comes to town. Taranov and his lover Elizaveta with her grown-up son want to enjoy a holiday at the sea-side. They never expected what melodrama awaits them here. The Undine is made up in the best traditions of long-running series with lost and found children, money, murder and, of course, fabulous love-story.