[These notes were made in 1983. I read it in a 1920s edition:]. Chambertin - sorry, Chauvelin - sets up an elaborate duel situation to get Percy Blakeney to France. Marguerite, with more nobility than sense, follows him and gets herself captured. A set of threats to innocent lives effectively prevent any dead-of-the-night escape attempts. And so, by brilliant subterfuge (the substitution of one piece of paper for another), our hero escapes once more, complete with (incidentally) a few more innocents rescued from Mme. Guillotine. The Formula strikes again - and a demn'd good one, too!