Her original plot :

"Well, this character, riding along at dusk, probably to stay with a friend comes to a toll-gate and can't get the gate-keeper to show himself. Finds this person in extremis, distracted wife in attendance, and takes over his duties for the rest of the night. (Now, whether he did this out of kindness, or because the gate-keeper had been Done to Death - which I think happened -
there's a general air of Fear and Mystery, which naturally intrigues our gallant Captain - or major - I can't tell you; but I incline to think the latter was the way it was.)

Next morning, bright and early, he has to go out (unshaved) to open the gate to none other than Our Heroine, Nell Stornaway ... Well! Our Hero is struck all of a heap by Nell and instantly decides to go on keeping the gate. All sorts of things happen - though exactly what I don't know. I rather think Henry Stornaway is carrying on some highly improper and illegal business but what it was I'm damned if I can discover. Furthermore, Our Hero, little though he knows it, has succeeded to his Cousin's Earldom, said cousin having had an accident.....Another cousin....having discovered (by means as yet unknown) where Our Hero is lurking, tries to do him in.

So this is why there is the scene at the Earl of Saltash's dreadful
betrothal party at the beginning of the book - with all the characters which we are introduced to and never appear again except his mother and sister. Also the intended villain was to be Lucius Staple, John's "jovial but wicked cousin".

~  The Private World of Georgette Heyer by Jane Aiken Hodge