Inspector Lestrade calls Holmes to the murder scene to examine something odd. Lucas bled over a drugget, and the blood soaked through it, but curiously there is no bloodstain on the floor under the drugget. However, there is one under the opposite edge of the carpet. It can only mean that the constable guarding the crime scene has been foolish enough to let someone in and leave them alone while they moved things in the room, including the carpet. Holmes tells Lestrade to take the constable to a back room and obtain a confession, which he does vigorously. Meanwhile, Holmes pulls the unfastened carpet aside and quickly finds a hiding place in the floor, but it is empty. The errant constable tells Holmes that the unauthorized visitor was a young woman. She apparently fainted at the sight of the blood but had left while the constable went out to fetch some brandy to revive her. As Holmes is leaving Lucas's house, he shows the constable a photograph, and he recognizes it as the visitor.