When aspiring inventor Isaac Turner visits the National Archives in Paris to receive a special honour, his moment in the spotlight is thrown into chaos by an assassination attempt on infamous businessman Balthazar Blaise. But when Isaac and his friend Hattie see a boy vanish from the crime scene without a trace, they suspect there’s more to the attack than meets the eye.

As they investigate, Isaac and Hattie are drawn into a heart-stopping adventure through secret and forgotten parts of the city, hunting a stolen letter, a missing sister, and the legend of a map which holds the key to untold fortune buried beneath the streets of Paris.

But with ruthless treasure hunters on their tail, the chase for answers becomes deadly. Can Isaac and Hattie untangle the city’s secrets before it’s too late?