The Chink in the Armour by Marie Belloc Lowndes

A small, shiny, pink card lay on the round table in Sylvia Bailey's sitting-room at the Hotel de l'Horloge in Paris.

She had become quite accustomed to finding one or more cards -- cards from dressmakers, cards from corset-makers, cards from hairdressers -- lying on her sitting-room table, but there had never been a card quite like this card.