It was late, nearly midnight, when I returned from an arduous day at Scotland Yard. The gas lamps cast long shadows on the cobblestone streets, and the air was thick with a fog that clung to my coat. As I approached 221B Baker Street, I could feel the weight of the day's investigations bearing down upon me. Reaching into my coat pocket, I retrieved the familiar key, its brass cool to the touch. With the precision born of countless repetitions, I fitted the key into the lock and twisted the doorknob. The door creaked open, and I stepped inside.