Vodník is the fourth and penultimate series of the television miniseries from the Detectives of the Holy Trinity cycle. In her spare time, Marie Výrová independently investigates a case long closed by the police involving the incomprehensible murder of a small child on the outskirts of Olomouc, which took place more than twenty-five years ago. Disturbing testimony from a witness to the long-ago tragedy prompts Marie Výrová to revisit the hopeless case and attempt to clear the unjustly convicted perpetrator.