The story begins in foggy London with two friends lodging in an old inn; a theft at Rotherhithe of an ornate set of jewels draws them into a layered investigation. Through letters, unexpected visitors, a foreign client, and a treasure hunt they follow contradictory leads, uncover hidden relationships and secret possessions, and sift through misleading clues such as a mysterious black bag. Suspense builds as suspicion shifts among acquaintances until evidence is brought to light, the responsible party is revealed, and the tangled affairs are settled, bringing calm after the storm.