MostlyDelores

Umpteenth re-read. I love this book. Nell is one of Heyers older, sensible heroines, John is steady as a rock but very nosy and delighted to stumble across mysterious and sinister goings on. Heyer is in top-form here, there are a host of memorable secondary characters, and the language is simply wonderful.

John to his mother: 
"I don't mean to offer marriage to any girl who don't give me a leveller. So I daresay I shall remain a bachelor, for they don't--any of 'em! And if one did," he added thoughtfully, "It's Lombard Street to a China orange you wouldn't take to her!"

A little while later: 
He stood as though stunned, for he had received his leveller at last.
*dreamy sigh*

An exchange between John and a farmer:
"What kind of knock-in-the-cradle do you take me for, dry-boots? You hand over the half of a fiddle!"
"How was I to know you was a downy one? I thought you was a cawker."
"You go and milk a pigeon!"

Joe the groom to John:
"I should say as there's three of 'em as needs watching. Holt--he's Mr. Henry's man--ain't no better than a clunch--and oyster-faced at that!--but Roger Gunn, which calls himself Coate's groom, is a regular ding-boy, or I never seen one! Whatever it is them pair o' shog-bags is up to, he's in it, up to the chin!" 

Nat Coate at the local pub:
His fancy had prompted him to sport a striped toillinette waistcoat under a coat of corbeau-cloth, and this combination, worn, as it was, with breeches of Angola cloth and hunting-boots with white tops, so powerfully affected the Captain that for a full minute he sat with his tankard halfway to his mouth, and his gaze riveted upon the astonishing vision. 
Say. No. More.

Joe the groom about one of the bad guys:
"Lord! he looks like a strained hair in a can!"