In this breathtaking adventure, Zélie and Jules face a deadly race to solve a family mystery and a vicious crime that stretches from the jungles of Calcutta to the sewers of Paris. Zélie is often accused of being a witch, but she doesn't believe in magic. Until Jules climbs up from the reeking Parisian sewer and hands Zélie the golden locket he discovered there.

The locket once held the magical Snakestone, and Zélie knows that if she can find the stone, she might also find her missing father. But a dangerous secret society are equally desperate to get their hands on the Snakestone and its powers. With their lives under threat, Zélie and Jules embark on a desperate hunt for the treasure, facing strange riddles, a mysterious circus, and the miles of murky tunnels that twist beneath the ancient city above...