A girl poisoned into isolation meets a thief who treats her like she's worth saving, and the show never wavers from that core promise. Every heist, every enemy, every revelation about what she actually is circles back to one question: does she deserve to exist outside that mansion. The romance isn't decoration, it's the entire spine holding everything together, and the show knows the difference between a love story and a reason to keep fighting.

Cardia lives alone in an abandoned mansion on the edge of London, keeping a promise to her father, Isaac. A poison in her body rots or melts anything her skin touches, and the locals call her a monster. Her memories are hazy, reaching back only to that last talk with her father two years ago. When the Royal Guards break in to seize her for the power of the Horologium, the eternally beating heart in her chest, the gentleman thief Arsène Lupin rescues her and vows to steal her heart. Traveling with Lupin and his companions, Cardia sets out to find her father, learn his rumored ties to the terrorist group Twilight, and uncover the truth about her lost memories and her condition. The show blends action, adventure, fantasy and romance.