In The Cabinet of Dr. Leng, Constance travels back to the late 1800s to stop the notorious serial killer Dr. Enoch Leng. She hopes to prevent the deaths of her siblings by thwarting his plans. However, facing one of the era’s most cunning and malevolent figures, survival becomes uncertain. Meanwhile, in present-day New York, Agent Pendergast races to reunite with Constance before she becomes trapped in the past permanently.