The Five Knots by Fred M. White

Beatrice and Wilfrid looked at Flower in astonishment. He did not seem to heed until his dull eyes met theirs and saw the question which neither dared to ask.

"A sharp, sudden pain," he gasped, "a pain in my head. I expect I have been working too hard. It has gone now. Perhaps it isn't worth taking any notice of. I am told that neuralgia sometimes is almost more than one can bear. So this is the piece of string the fellow was using, Beatrice? I am afraid I can't disbelieve you any longer. I am sure that there is no string like this in the house. In fact, I never saw anything like it before. What do you make of it, Dr. Mercer?"