“I just need to find my coat,” he shot back. -- too soon. Not enough build-up, not enough anger. "shot" doesn't really work for me. Rather than "shot back", perhaps try "retorted" or "excused", since it does sound more like he's making an excuse than like he's snapping.

"piles of discarded clothing scattered on the floor" -- the clothes aren't scattered, they're in piles. Or they're not in piles, they're scattered. I don't see how it could be both. Pick one.

"His voice trailed off into a stream of French." -- sounds weak, especially after all the French already written. Maybe try "trailed off into muttering".

"holding out his coat she’d been carrying" -- "the coat", or "his coat, which she'd".

"by Etienne’s insistence" -- second "by" in one sentence cuts the impact. Replace this one with "at".

"She smacked him upside the head." -- LOL. Not a good line for a Serious Story. Not terribly descriptive, either.

"I think you’d be" -- "I'd", or alternatively "you should be".

"smashing a cat" -- "crushing" reads better. "smashing" is both awkward and a hideously unpleasant (and inaccurate) image.

"said nothing to the change in plans" -- "about", not "to". A change of plans usually isn't very talkative or personable, I wouldn't say a word to one either. :P

"garish half-light" -- explain. How can a half-light be flashy and tasteless? Look for another adjective.

"Elizabeth nodded, jaw set and a cold smile on her lips" -- you left out the period. I'd also rephrase after the comma, perhaps to "with a set jaw and a cold smile" or to "smiling coldly, her jaw set".

"whippy skirt" -- doesn't sound right. It shouldn't whip about indoors. Or do you mean it's whip-slender, like a dress made of rope-bondage? O_o

"catching the looks in her direction." -- wat. Rephrase/remove.

"the restaurant" -- I thought it was a hotel?

"You heard from" -- too informal for the context. Put "Have" in front.

"Yes, I did." -- wrong tense. "I have", not "I did". The rest of this line is rather poor and makes little sense.

"he lived in London eight months out of the year since he was ten" -- I'd say "he's lived" and "since the time he was" or "since the age of"

"Let’s do this again soon, hm?" -- I get it, but it looks bizarre in writing. You should find another way to express that.

"“Surely,” she replied." -- "surely" sounds strange there. Try "sure" or "of course" or "naturally".

"Etienne kept watch" -- another missed period. I'm seeing a pattern. It's the horizontal bars messing you up, right? You can do without most of them, honestly, since there's no real change in perspective. Be more sparing.

"flip her body around enough to swing her leg around to kick him" -- too cumbersome. Drop "to swing her leg around".

"a string of Latin spilling from his lips" -- the second time magic has been used with insufficient fanfare. You're writing from the mage's perspective, right? Mention that it's a spell, or we're all still expecting spy-novel type writing and getting weirded out by inexplicable happenings.

"all the while" -- unnecessary. Drop it.

"We know you’re a mage." -- the moment of revelation is a little too late. Keep this line where it is, but still mention the fact earlier.

"the bloody mess of flesh and shattered bone" -- uhh ... cold air did this? Huh?

"The pushed their way" -- "they".

I like this, especially the way it ended. But I'm disappointed because I feel you could have written it so much better. I think your skills have gotten rusty since your last update. You'll just have to write more, won't you? ;)