After Mary's death, John grieved for her very much and stopped communicating with Holmes. One day, Mrs. Hudson called him in tears and begged Watson to come and, as she said, to straighten Sherlock's brains. He stopped eating and sleeping. In addition to his breakdown (drugs), he also began to leave the house. The woman was very worried about him and John too, he just didn’t want to admit it.

And now a man is standing at the door of his old apartment, knocking on it.