The Hands of Healing Murder

After dinner, Dr. Adam Cotton settled in a chair by the fireplace to read, while his guests made up two tables of bridge. Engrossed in their game, no one left the room. And the two servants who were sitting in the hallway all evening, deep in conversation, claim that no one entered the room. But someone inserted a small surgical scalpel into the parietal bone of Dr. Cotton's temple, killing him instantly.