The stranger flirting with Valentine St. James at the costume ball has guts. Sure, he wears a disguise, but his moves are especially conspicuous because partygoers expect an announcement on this night of Valentine's engagement to another man.
Still, the stranger steals Valentine away from the ball, and she falls into his embrace. Imagine her embarrassment when she discovers that her betrothed, Lord Hawkeston, is actually behind the mask. It's a dirty trick, for which he doesn't repent. To not forgive him means denying her strong attraction. How long can she hold out?