A clinic for the mentally ill, lost in an oak grove near a swamp... Young psychiatrist Vera Arngolts was delighted at the proposed place: a good salary, there was an opportunity to work on a dissertation, and she and her husband were given a separate cottage. The girl will have to deal with dangerous criminals who are under compulsory treatment, but helping these people is her job... Vera noticed strange things right away. For some reason, she was not allowed to communicate with some patients and was not allowed into the laboratory where some secret experiments were being carried out. By chance, Vera found out that her predecessor had drowned in a swamp, and became convinced that something terrible and incomprehensible was happening in the clinic... Why are patients dying here and doctors disappearing without a trace?