Trying to remember title -- spoiler

Re-reading "Regency Buck," where the duel the younger brother is about to fight is stopped, I was reminded of a similar situation in another Heyer book, where the hero actually draws the would-be opponent into a duel with himself and wounds him before he can fight the brother. I can't place the book, though. Can anyone remember which it is?

I remember the book, but now I can't spell the title, how I wish LT had spell check, my need for spell check is a failing in me not LT.

Masqeraders

Oh thank you, yes, The Masqueraders! And of course Sir Tony had extra reason for not letting the "brother" fight the duel. . .