"My last crime was a Christmas crime, a cheery, cosy, English middle-class crime; a crime of Charles Dickens. I did it in a good old middle-class house, a house with a crescent of carriage drive, a house with a stable by the side of it, a house with the name on the two outer gates, a house with a monkey tree. Enough, you know the species." How does Father Brown solve the theft of three gorgeous, large diamonds by a boastful thief?