Derek Capel

In the short story The Coming of Mr Quin, Derek Capel was the former owner of the country house named Royston. Mr Capet had comitted suicide ten years before the events in the story.

At the time of his death he had announced to his guests that he was engaged to be married. He hadn't told anyone who the woman was but seemed happy about the prospect. Yet just a few minutes after the announcement, he had gone up to his room and shot himself. The reason for his suicide was a mystery. Discussing the circumstances of the suicide and divining the reasons for it forms the main part of the plot of the story.

In The Love Detectives, Mr Satterthwaite tells Colonel Melrose that it is due to Harley Quin that the mystery was solved.