Kaito Tanaka, a young Japanese man obsessed with detective stories like Sherlock Holmes and the hidden world of the occult, meets his end in a tragic work accident. When he regains consciousness, he awakens in a crumbling mansion in a world eerily similar to 1830s London—but not quite his own Earth. Transformed into the enigmatic Lord Valerius Thorne, with an otherworldly appearance—tall and pale, with piercing red eyes, long obsidian-black hair, and an immortal body—he discovers his new invulnerability by chance. Embracing this fate, Valerius sets out to become a detective unraveling supernatural cases in the shadowy underbelly of Victorian society.