In early 1847, the young Quebec city doctor, Lauchlin Grant, struggles to extract a living from his boring practice and pines over his childhood sweetheart, Susannah. She is now the wife of a prominent journalist, Arthur Adam Rowley, who has charged Lauchlin with her care, while he travels in Europe to report on the ghastly potato famine in Ireland and his predictions for its effects on immigration.

Even as Rowley's letters are read at home, waves of starving Irish land at Grosse Ile in the St. Lawrence River where thousands are ill or will sicken of ship fever (typhus), and die. Lauchlin is called to help at the quarantine station. Of the hundreds in his care, he rescues only Nora. Having lost her family, Nora decides to remain as a nurse, because she is now immune.

Lauchlin sees Susannah only once more, learning that she too cares for victims of typhus, which is also ravaging the mainland, despite the quarantine. He senses her unspoken love for him and, filled with an inner peace, returns to Grosse Ile, only to contract typhus and die. Nora takes the doctor's belongings to Susannah's home, hoping to meet the woman whose name he had mumbled in his delirium. Instead, she finds Susannah's newly returned husband dreading the loss of his now dying wife.