This is quite a good classic mystery story and one of the better offerings in the Holmes saga. It involves a mysterious murder of a young secretary. He has been stabbed in the neck with a letter opener and has bled to death, his dying statement: "Professor...it was she." The secretary has also grabbed a golden pince nez (those old fashioned spectacles that sat on a person's nose). The professor in question is a bed ridden, chain-smoking historian. He is a harsh man with little patience. Holmes has been called in, assisted by brother Mycroft (apparently Edward Hardwicke, the Watson of the series, was unavailable for this episode). Holmes has been approached by a young police detective, who has produced a layout of the house and offered a few opinions. Of course, the two brothers are incensed by his basic incompetence. This leads to an investigation that banks on how someone could commit a murder in this house and not be seen by the housekeeper or the maid (who discovered the body). There is also a subplot about a women's temperance group, whose leader has become a possible suspect. There are also forces going back to events long ago involving an attempted revolution. This is also the time when Mycroft quotes their father concerning eliminating the impossible, hence, leaving behind the truth. The ultimate maxim of Holmes. Excellent performances all around, especially the Professor, played by great British stage actor Frank Finlay.