The story opens in Amsterdam during a ferocious thunderstorm, where the eccentric scholar Cornelius Pamp and his anxious friend Balthazar Van der Lys take shelter in Balthazar's home. Balthazar is deeply in love with the wealthy Suzanne Van Miellis and plans to present her with a treasured keepsake: a delicate flower preserved inside a gold and black-pearl locket. However, when Balthazar goes to retrieve the locket from his desk, he discovers the room ransacked, his savings stolen, and the locket missing. The local police commissioner, Tricamp, arrives to investigate the crime with rigid, misguided logic.
Despite the lack of physical entry points, Tricamp quickly fixes his suspicions on Christiane, a gentle young orphan raised in the household whose past includes a family of pickpockets. As the police commissioner builds a seemingly airtight circumstantial case against Christiane, she falls into deep despair and attempts to drown herself in the canal, only to be rescued at the last moment. While Tricamp relies on flawed human deduction, Cornelius approaches the mystery through rigorous scientific observation.
Examining the physical anomalies in the room and the strange state of the household objects, Cornelius realizes that human hands never committed the robbery at all. The culprit was a powerful ball of lightning that struck the house during the storm, fusing metals, melting glass, and inadvertently transforming the stolen valuables into a solid lump of precious ore. With her innocence brilliantly and scientifically proven by Cornelius, Christiane recovers from her ordeal. In the end, the misunderstanding is completely resolved, and the two friends look forward to their respective weddings, bringing peace and happiness back to the Amsterdam household.
