A review by katherinethatsmyname
The Mysterious Mr. Quin by Agatha Christie

Mr Satterthwaite, a rich man who knows everyone, plays the detective role, assisted by his muse, the mysterious Mr Quin, who appears whenever there is a problem to be solved, and subtly aids Mr S in its conclusion . Mysterious to the point of supernatural, the stories all revolve around love and death. Apparently the character is inspired by Harlequin and Columbine, which I must research.