Katherine
A fictionalized account of Katherine Swynford and John of Gaunt's decades-long love affair through plague, war, and court politics in 14th-century England. Seton writes historical romance with the conviction of biography; the love story is all the more powerful for being grounded in fact. The template for the American historical romance novel.
Five hundred pages of pageantry, plague, and penance, with Seton stopping the romance regularly to inventory feasts, genealogies, and gowns. Katherine herself stays saintly past the point of credibility; the decades-long affair gets a 1950s scrubbing, anguish without much appetite. By the long religious-atonement stretch near the end you may feel you have done the penance yourself.
The case for it and the rest of the canon open with Pro.
