What secrets lay beneath Parisian Streets? And who will kill to keep them?

When a malfunctioning automaton runs full force into their locomotive on the new Paris-Orléans railway, Jacqueline Duval and her bohemian twin sister Angélique Laforge become embroiled in a mystery deeply rooted in their tragic past.

A polytech and famed engineering prodigy, Jacqueline is fascinated by the metal man, even more so when she discovers that it is powered not by steam, but by the supernatural. Her investigation puts the sisters on a path both dangerous and mysterious as they must foil a plot to employ the dead to power a mechanical army aimed at international conquest.

Aid comes from unexpected sources as the twins rush to avert this engineered war, but will they be in time?