When 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.

The year is 1847 – “Black 47” – and 100,000 Irish emigrants are fleeing to Canada to escape starvation. They bring with them the dreaded “ship’s fever” and soon Canadian ports are overflowing with the sick and dying.

Lewis’s youngest son Luke has aspirations to be a doctor. He volunteers in the fever sheds in Kingston and when he finds a green ribbon on the lifeless body of a patient, he is intrigued by the strange coincidence. He enlists his father’s aid to uncover the mystery, a tale of enmity that began in Ireland and leads them to the heart of the criminal underworld of Toronto, where the final acts of vengeance play out against the tragedy of the fever sheds.