It's Oct of 1885. Author Robert Louis Stevenson’s health is failing and his work on his latest novel has stalled. Because his finances are in near-ruin, Stevenson agrees to write a "Gothic shilling-shocker" for his publisher despite an impossibly short deadline. 

When he is visited by a mysterious and sinister figure in the theatre of his imagination, Stevenson becomes increasingly obsessed by the notion of evil that can live under a veneer of respectability. 

Though his wife Fanny and his lifelong friends try to support him, he gives himself over to his shadow self, spiraling downward into temptation, selfishness, and addiction before finding his way back to reconciliation and emerging with the manuscript Strange Case of Dr. Jekyll & Mr. Hyde.