Paris. 1889 Technological progress has breathed new life into the city, but ancient secrets are still hidden in its depths. No one knows them better than treasure hunter and wealthy hotel owner Severin. When the powerful Babylonian Order forces him to join the search for one of the lost artifacts, Severin has the opportunity to take possession of a treasure he could never have dreamed of.

To discover the artifact the Order is looking for, Severin turns to a group of very unusual people: a girl engineer who needs money; a historian exiled from his family; a dancer with a murky past and a gardener with a rare gift. Together they will explore the dark belly of Paris. But something hidden in the labyrinth of the catacombs can change the course of history forever...