Martin Wroath is found dead in his cottage after apparently having committed suicide. Barnaby is not convinced that it was a suicide and when Wroath is found to have a large amount of anti-depressant in his body it is apparent that he would have been unconscious at the time. On further investigation, Barnaby finds himself at the nearby Mercy Park cottage hospital, which is run by an old acquaintance of his, Dr Jane Moore. When one of the staff is killed, Barnaby and Troy must find the murderer before they can strike again...