Miss Morstan had remained behind with the frightened housekeeper.
The third flight of stairs ended in a straight passage of some length, with a great picture in Indian tapestry upon the right of it and three doors upon the left.

Holmes advanced along it in the same slow and methodical way, while we kept close at his heels, with our long black shadows streaming backwards down the corridor.

The third door was that which we were seeking.

Holmes knocked without receiving any answer, and then tried to turn the handle and force it open.

It was locked on the inside, however, and by a broad and powerful bolt, as we could see when we set our lamp up against it.