Comic book legend Jacques Tardi's graphic novel provides the inspiration for this loose big screen adaptation from France, from screenwriters Franck Ekinci (who-codirects with Christian Desmares) and Benjamin Legrand, with graphic design work on the film by Tardi himself. It's a steampunk alternate world where Earth's has progressed little scientifically since the Industrial Revolution, primarily because scientists have been outlawed, and they've begun disappearing en masse.
Most of the film is set in that alternate Paris in 1941, under the rule of Napoleon V, where much of the power supplied to the world comes from pre-fossil fuels like coal, charcoal and wood from the rapidly dwindling forests of the world. April is an inventive orphaned woman with a smart-alecky talking cat named Darwin. She lost her scientist parents at a young age when it was discovered that they had possibly invented something called the Ultimate Serum, a chemical cocktail that makes its imbiber rejuvenated, cured of disease, and virtually immortal — something that could tip the global war for resources in France's favor should they be able to create their own invincible super-soldiers. April is being closely monitored from several interested parties in case she happens to stumble on the potent concoction, or invent it on her own, with the tenacious French policeman, Gaspard Pizoni, on orders to observe her every move. April makes that discovery, but finds an even larger one emerges that threatens to shift the balance of world power in an entirely unexpected direction.