The Adventure of the Golden Pince-Nez

"The Adventure of the Golden Pince-Nez", one of the 56 Sherlock Holmes short stories written by Sir Arthur Conan Doyle, is one of 13 stories in the cycle collected as The Return of Sherlock Holmes.
One wretched November night, Inspector Stanley Hopkins visits Holmes at 221B Baker Street to discuss the violent death of Willoughby Smith, secretary to aged invalid Professor Coram. Coram had dismissed his previous two secretaries. The murder happened at Yoxley Old Place near Chatham, Kent, with a sealing-wax knife of the professor's as the weapon. Hopkins can identify no motive for the killing, with Smith having no enemies or trouble in his past. Smith was found by Coram's maid, who recounts his last words as "The professor; it was she."