50. What is the reason that the room is locked in the tavern?

According to the tavern-keeper's son, the room was locked because it was haunted. From the text, we can infer that someone is staying in "Number Two".

The tavern-keeper’s young son said it was kept locked all the time, and he never saw anybody go into it or come out of it except at night; he did not know any particular reason for this state of things; had had some little curiosity, but it was rather feeble; had made the most of the mystery by entertaining himself with the idea that that room was “ha’nted”; had noticed that there was a light in there the night before.