OK, I think I've solved my problem. Not entirely happy with the outcome, but I think it'll work:

Those of you who followed a question I posted on Natter and Bitches about what might make a 19th century woman logically conclude she was infertile may remember I moved Lucy from 1810 to 1809 to make the 1811-12 setting of Anna be two years after Anna's marriage to Lucy's cavalry officer cousin Sebastian. At the start of Lucy, Sebastian is away from his regiment recuperating a leg wound that's left him temporarily unable to sit a horse. When I moved the setting to 1809, I thought it would work perfectly to have him wounded on the retreat to Corunna, since all the troops involved were evacuated back to England anyway, returning (so I thought) a few months later. All I'd have to do is make him not well enough to rejoin his regiment right away.

Except I remembered after already starting my rewrite that I really needed to do due diligence and make sure the regiment I'd picked for him was more or less where I needed it throughout both books and the two years in between. That's when I discovered that, best as I could piece together from brief online regimental histories and lists of battle honours, the cavalry regiments that were at Corunna, unlike the infantry, didn't return to the Peninsula until 1812 or 1813. Cue writerly angst. I didn't want to make Sebastian an infantry officer, though I could if I had to. And I really didn't want to invent a fictional regiment, because it just seems kinda sloppy to put Jack in a real one and not do the same for Sebastian.

So. After squinting at the list of battle honours for awhile, I noticed the 16th Light Dragoons were absolutely everywhere I needed them to be BUT Corunna. Poking around Google eventually revealed they arrived on the Peninsula in April 1809 and stayed for the duration. Problem is, Lucy opens in May 1809. My current idea is that Sebastian sustained some kind of accident (broken leg?) or illness around February March 1809 that left him in no shape to depart with the rest of his regiment. It changes him from "romantic wounded veteran" to "prickly and somewhat embarrassed at being absent from his unit at such a time," but I think my plot will still work. Right?

Actually, considering Sebastian's personality, I think it works even better. Let go the reins and tossed off his horse, perhaps, in front of superior officers, with a cracked tibia, or something?

Hmm. I don't want Sebastian to actually be an incompetent rider or anything, but I'm also not sure I want to give him a straightforward good rider fall like I gave James in the first chapter by having Ghost get spooked (pun intended) and refuse a fence. Maybe there's a new horse who's a bit of a brute, and Sebastian thinks he can be the one to tame him and gets thrown in the process?

Yes, exactly. Not incompetence: overreaching. That's where I was going with it.

And if he's afraid he's embarrassed himself in the eyes of his fellow officers, it'll make him all the more eager to court a superior officer's pretty, rich cousin. I like this.

How do you decide who to kill?(Because, ok, it's noir. Somebody's ticket's getting punched. ) But I can't decide if it should be Mysterious Rich Hottie Client's Sister or if someone should die in the quest to protect MRHCS and she's in more of a "Can they save her before it's too late?" kind of deal. Most of my fiction doesn't go in for killing...except with sharp words.

erika, it depends. How annoying is the sister, how vital is she to the continued happiness of the hottie brother?

Hmm. In my work I mostly kill people just to streamline the plot and get them out of the way (and, boy, is it easy to do in the late 18th and early 19th centuries--French bullets and consumption and childbed fever, oh my!). But I think you want to go for the most important person dying that you can make the rest of the story work without. IOW, kill the sister if you can, IMO.

I could, defintely...there are still many ways to take a person out in this century.

Yep. The beauty of the past for a death-minded writer is it's just so easy to kill people young without necessarily resorting to violence.