The mysterious Mr. Quin

The Mysterious Mr Quin is a short story collection by British writer Agatha Christie, first published in the UK by William Collins & Sons on 14 April 1930 and in the US by Dodd, Mead and Company later in the same year. The UK edition retailed at seven shillings and sixpence (7/6) and the US edition at $2.00.
Each chapter or story involves a separate mystery that is solved through the interaction between the characters of Mr Satterthwaite, an elderly socialite, and the eponymous Mr Quin who appears almost magically at the most opportune moments and disappears just as mysteriously.
In her foreword to the collection, Christie states: "Mr Quin, I consider, is an epicure's taste." (HarperCollins 2017 p. vii) Her husband Max Mallowan described the stories as "detection written in a fanciful vein, touching on the fairy story, a natural product of Agatha's peculiar imagination." Christie's favourite stories were 'The World's End', 'The Man from the Sea' and 'Harlequin's Lane'. (p. viii)

(This summary is from Wikipedia.)