The Attenbury Emeralds (The Lord Peter Wimsey and Harriet Vane Mysteries‪)‬

The recovery of the magnificent gem in Lord Attenbury's dazzling heirloom launched a shell-shocked young aristocrat on his career as a detective in 1921. Thirty years later, a happily married Lord Peter has just shared the secrets of that mystery with his wife, the detective novelist Harriet Vane. Suddenly, the new Lord Attenbury—grandson of Lord Peter's first client—seeks his help to prove who owns the emeralds. As Harriet and Peter contemplate the changes that the war has wrought on English society—and Peter, who always cherished the liberties of a younger son, faces the unwanted prospect of ending up the Duke of Denver after all.