In this case, the book unfolds with Lord Cardross (Giles) firmly scolded Lady Cardross (Nell) for some rather profligate spending in the last month. All is forgiven, but he at least asks her to be careful in the future. Well, Nell had overlooked one receipt, which happens to be a for a dress that was worth the exact amount that she lent to her brother, which of course she shouldn’t have, because he’s a gambler. So she can’t tell Giles, he eventually figures out something is up, confusion reigns, bladdy bladdy blah.
Oh, and Giles has a younger half sister who is a confirmed ninny and wants to marry someone wildly unsuitable. Fortunately, he’s too sensible to elope, but there’s still drama.
Yeah, not one of my favorite Heyer books.