The player assumes the role of Mary Clarissa Christie. Mary has heterochromia eyes, her right eye is gold while her left eye is blue. She originally had blue eyes but her right eye changed colours one year prior to the game's events and she has been seeing strange visions since.

The year is 1905 in the capital of the British Empire, the Engine City London, where the air is so thick with smoke that a mere glimpse of the blue sky is considered a miracle. The protagonist, Mary Clarissa Christie, is a girl living by herself while her mother works abroad. She attends university with her friends, Angelica Derleth and Charlotte Bronte, and lives a peaceful life.

However, through a chance encounter, she finds herself drawn into another side of London- spoken of only as rumors of "Metacreatures" who roam the night and attack people. She forms a contract with a strange man in a black suit, known as 'M', and begins to help him hunt these creatures...