- Director: Viktor Taus
- Writer: Petr Jarchovský; Michal Sýkora
- Producer: Jan Stern
The Water Goblin is the fourth, penultimate series of the television mini-series from the Holy Trinity series Detectives. Marie Vyrová, in her free time and on her own, is investigating a long-standing case of an incomprehensible murder of a small child on the periphery of Olomouc, which took place more than 25 years ago. The disturbing testimony of the actress of the long-time misfortune causes Marie Výro to reconsider the hopeless case and try to cleanse the unjustly convicted culprit. The story of Vodnik takes place in two timelines: in the days just before the revolution at the end of the communist era in the late 1980s and now. In the first instance, the criminal case of Communist Czechoslovakia under the command of Major Voženil deals with the case. At present, Mary reveals serious deficiencies in the investigation of the then police and reveals the reasons that led to them.