He knew that the fingerprint hadn’t been on the wall when he first looked at the corridor and he
knew that McFarlane’s walking stick was in the house. He thought that the housekeeper must have
hidden the walking stick. He guessed that Oldacre was hiding in the house and had used his own
blood to put on the stick. He worked out that Oldacre had used sealing wax to make an impression
of McFarlane’s finger so that he could make McFarlane’s fingerprint on the wall. Holmes paced up
and down to measure the length of the outside of the house and then he did the same thing in the
upstairs corridor. He found out that the corridor was shorter than it should have been so he knew
that there was a hidden room.