A Puzzle in Pearls — John Creasey

A stolen necklace has British detective Patrick Dawlish running in circles to find the culprit in this classic Golden Age mystery.
 
A famous jewel thief has struck again, stealing a fortune of gems from Lord Hillmorton and kidnapping his daughter to ensure his silence. But there's one man to call when there are no other options: Patrick Dawlish.
 
Hot in pursuit, Dawlish, his wife, and Cedric Forbes find themselves caught between a notorious gang of thieves and a quirky family who may or may not have their own part to play in the crime. As a strand of valuable pearls changes hands, it's up to Dawlish to orchestrate a plan to root out the fakes from the genuine article -- and bring the innocent home alive . . .