The bloated corpse of a man dressed in women's clothing washes up on the shore of Lake Ontario near Thaddeus Lewis's home. Nothing is found on the body except a small scrap of green ribbon. It's 1847 - "Black '47" - and 100,000 Irish emigrants are fleeing to Canada to escape starvation. The emigrants bring with them the dreaded "ship's fever," and soon Canadian ports are overflowing with the sick and dying. Lewis's youngest son, Luke, volunteers in the fever sheds. He finds a green ribbon in the lifeless hand of a patient named John Porter. Luke uncovers a tale of enmity that began in Ireland, and enlists Thaddeus's aid in trying to discover what happened. Their search leads them to the heart of the criminal underworld of Toronto, where the final acts of vengeance play out against the tragedy occurring in the fever sheds.