On leaving the Italian convent in which she was educated, Una Thoreau set out for Paris to join her father in Montmartre. She arrives to discover that her father is dead. Alone in foreign city, her father's picture dealer, Philippe Dubucheron, befriends her and takes Una to a party at the Duke of Walstanton's. Una is unaware that her presence there is deviously planned. The Duke is to choose between two women - Una and Yvette Joyant, a sophisticated and notorious demimondaine.