London, 1872. Irene is worried about her father. During the winter, Leopold Adler's mood becomes increasingly melancholic. To lift him out of his dark thoughts, a friend invites him to spend a few days in the countryside, in a lovely farmhouse with a large garden. Irene will devote her time to literature and horseback riding, while her father will participate in a fox hunt. In this seemingly peaceful 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 as the news of a gruesome murder unsettles the village, the three friends, once again together, begin to investigate a new case rooted in dark and strange events of the past.