Villa Diodati, Lake Geneva, 1816. The dark summer that birthed a monster. Eighteen-year-old Mary Shelley has fled London with her lover, Percy Shelley, and her sister, Claire. Tormented by Shelley's betrayals, haunted by the loss of their baby and suspicious of her sister's intentions, Mary seeks a refuge. But Lord Byron's villa, lying under ominous, ash-shrouded skies, feels more like a trap. When Byron suggests each guest write a supernatural tale, Mary is as drawn to the challenge as she is, unexpectedly, to Byron himself. And so an idea begins to form in her mind. It spills out of her in thick, black ink. A thing given life is before her. Day and night, it possesses her. Her heart, her desires. But is she in control, or is it?