Celine de Croix is a young viscountess without inheritance or power. To escape her role as a puppet of her uncle the Duke, she flees from a continent dying of plague on an expedition to a mysterious island. The inexperienced diplomat is unaware that in addition to civil strife and the black market for slaves, the production of opium and deadly alchemical weapons is thriving in the colony. The head of the expedition, Captain Vital, recognizes his love in Celine - the mysterious mermaid who comes to him in his dreams. But is there something more behind the external resemblance? Or the Viscountess is just an arrogant aristocrat who, due to her own illusions, does not understand what a dangerous political game she is interfering in. And all their plans go to the Sea Devil when a former friend’s pirate armada appears on the horizon...