The middle of the 18th Century! A time of revolutions, highwaymen and hairbreadth 'scapes. When men were real men absolutely everybody except Tony is dressed in fabulous sparkly lacy numbers at all timemarshals less of their apparent gender. (is it just me who thinks the Regency is lovely but would prefer some shinier clothes - I feel GH probably felt the same).
My major argument with Powder and Patch was that it had far too little plot, which explains why The Masqueraders is one of my favourite Heyers. We have the escape from the Jacobite Rebellion, the Missing Heir (see also Black Moth, Talisman Ring), Evil Abductor, "I love him but I'm not worthy of him", and that's before we get to the cross-dressing. For my money GH pulls this haystack of plots together brilliantly, with the grosser implausibilities covered over by Tremaine's outrageous character: anything particularly mad (or, in Letty's case, cruel) is explained by the fact that he's showing off.
When it comes to the romances I have (like GH) a terrible weakness for competent men, and Tony's ability to improvise/ride/duel etc wins me over, along with a beautifully judged approach to Pru: he loves her because she's strong but he wants to protect her anyway. It hits a rather atavistic romantic streak in me that few Heyer heroes come near. Is this just me? Does anyone else see the appeal, or is he just controlling and annoyingly "masterful"? GH is obviously going to great pains to put him in the right side of the line but does she manage?
And Robin/Letty? The secondary romantic couple are normally a bit wet in GH; are these two better or worse than normal? Is it remotely plausible that Letty would forgive him for his deceit? (though at least he tells her - IIRC one of the girls in False Colours never finds out)