Sofia Verbyana is a young, talented investigator who, after graduating from the academy, joins the police force as head of the particularly dangerous crimes department. She is enthusiastic, ready to defend the truth, sharp-minded, honest, and principled. But due to her lack of experience, she often makes mistakes and appears uncertain. Her meeting with forensic expert Pavel becomes another test for her. He is silent, sharp-tongued, and straightforward. Despite communication difficulties, Sofia and Pavel successfully solve the most complex crimes. And perhaps, without realizing it, they begin to feel something more than professional interest.

The Mavka, a mystical and dangerous forest nymph, falls in love with the biologist Lukyan instead of destroying him in the mysterious forest lake, where mermaids and other nymphs await men's souls. And they are ready to do anything to keep the Mavka on the dark side.