"The Learned Adventure Of The Dragon's Head" is a short story from Dorothy Sayers' book, Lord Peter Views the Body.
Lord Peter Wimsey, Dorothy Sayers's eccentric amateur sleuth, is saddled with his ten-year-old nephew while his parents are away overseas. As the two browse an antiquarian bookshop, the boy is attracted to the maps and pictures in a badly damaged copy of Cosmographia Universalis, an early description of the world. He buys the book, and shortly afterwards a strange man visits and offers Wimsey two hundred times what the boy paid. This leads to a "Boys Own" type adventure involving attempted robbery, Scotland Yard and a riddle leading to buried pirate treasure.
