Quick recap
Michael Stirling, a notorious rake, falls for Francesca Bridgerton at first sight, just before she marries his cousin John, Earl of Kilmartin. Michael keeps it to himself and becomes the couple's closest friend. In 1820, John dies suddenly, and Michael inherits the title he never wanted. Guilt-ridden, he leaves for India. Four years later he returns to London, and Francesca, set on marrying again and having children, realizes her old friend stirs something in her. The hard part is accepting she can love again without betraying John's memory. In the end, they marry.

