When his daughter Princess Ameena died, Rameses, the Egyptian Pharaoh, placed a necklace about her neck and swore that whoever took it thence should never rest in peace until it was returned. Some thousands of years later, Ameena's mummy was unpacked in the New York Art Museum and the necklace was discovered. The news of the discovery of the priceless relic reached the ears of a band of thieves and '"Diamond Mary" was dispatched to steal the necklace. She was successful in her mission, but the tremendous sensation caused by the theft made disposing of the jewels in America absolutely impossible. Accordingly Mary sailed for England, where she was joined by accomplished criminal "English Jim." Detective Imbert was engaged by the museum to conduct the search for the missing relic. Imbert followed Mary to England and had her arrested, but not before she had given the necklace to her confederate. The pair escaped to Paris, and there Imbert had "English Jim" arrested with equally futile results. Then he followed them to Venice, where they overpowered him after an exciting chase in gondolas. Then to Rome, where "English Jim" paid the penalty of his ill-spent life by falling from a roof in an attempt to escape the relentless sleuth. How Imbert gave up the chase in Naples and how he finally recovered the gems in New York there is not space to tell. Nor is there room to describe the wonderful historic settings in which so many of the scenes are laid. We can only mention Notre Dame in Paris, the Grand Canal, the Campanile and the Doge's Palace in Venice, the Forum, the Colosseum, and St. Peter's.
—Moving Picture World synopsis