Short story 'The Blue Cross' is Chesterton's first Father Brown mystery.
It 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.
Brown has been committing acts to draw the attention of the police (throwing soup, knocking over apples, smashing a window) and leaving an obvious trail for them to follow. Valentin takes this opportunity to emerge from hiding with the policemen and arrest Flambeau. Both Flambeau and Valentin bow to Father Brown's superior detective skills.