London, 1872. Irene is worried about her father. In winter, Leopold Adler's mood becomes increasingly melancholic. To pull him out of his dark thoughts, a friend invites him to spend a few days in the countryside, at a wonderful cottage with a large garden. Irene will dedicate her time to literature and horseback riding, while her father will participate in a fox hunt. In this seemingly tranquil environment, however, a mysterious man disappears. Irene immediately realizes that something suspicious is happening and sends a letter to Sherlock and Lupin asking for help. And while the news of a brutal murder unsettles the village, the three friends, reunited once again, begin to investigate a new case rooted in dark and strange events from the past.