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. The emigrants bring with them the dreaded "ship's fever," and soon Canadian ports are overflowing with the sick and dying and entire families are being torn apart. Lewis's youngest son, Luke, who has aspirations of becoming a doctor, volunteers in the fever sheds in Kingston. When he finds a green ribbon on the lifeless body of a patient named John Porter, he is intrigued by the strange coincidence. Though dealing with demons of his own, young Luke enlists his father's help to uncover the mystery, a tale of enmity that began back in Ireland. Their search 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.