Scotland Yard is tasked with ensuring that the recently widowed Lady Gwendolyn Avon doesn't smuggle an expensive necklace known as Avon emeralds out of England. Most of her late husband's estate was given up in death taxes and the police are sure she could sell them at a premium abroad. Inspector Benson is tasked with ensuring the jewels' safekeeping but when they are stolen from the hotel safe, it appears Lady Avon has a perfect plan.