The book that started it all. Anyone interested in writing romance novels (or fans of same) should read this book. It's not Woodiwiss' best, and contains a number of elements that would be considered serious taboos in today's romance novel world. However, the Flame and the Flower was the first romance novel of the kind we know today -- rather than fading to black or moving behind a closed door, Woodiwiss included sex scenes, with minimal euphemism and a connection to the emotional development of the characters. Before the Flame and the Flower, this did not exist.
Does the heroine make me cringe? A little. Am I uncomfortable that the hero and heroine are forced into marriage because a night of what was essentially rape led to a pregnancy? Yes. Do Woodiwiss's later works improve on said issues? Absolutely. But for historical value, this is a must-read.
For extra fun if you're a story geek like me, read this and then read the Elusive Flame, which is a story of the Flame and the Flower's son, published 25 years or so later. Extreme similarites (hero is a sea captain docked in London, heroine is in trouble, marriage of necessity/convenience, long sea voyage during which the couple gets to know each other, arrival in South Carolina...), but extreme differences that show the accepted sensibilities of the publishers and readers at the time these were published.