'The Blue Cross' is a short story by G. K. Chesterton. It was the first Father Brown short story and also introduces the characters Flambeau and Valentin. It is unique among the Father Brown mysteries in that it does not follow the actions of the Father himself, but rather those of Valentin. It was first published on 23 July 1910, under the title 'Valentin Follows a Curious Trail', in the Saturday Evening Post, Philadelphia. Re-titled as 'The Blue Cross', publication in London followed, in The Story-Teller magazine of September 1910.