That is an excellent book, and I agree with you about how hard the third act hits. If you’re interested, she has a couple other novels in the same setting (time-traveling historians): To Say Nothing of the Dog, a much more light-hearted Victorian-era farce that overlaps with events from the real-life novel Three Men in a Boat which is itself a good and funny read, and the two-parter Blackout and All Clear, neither of which I have read but are on my list to get around to someday.
That is an important one and I’ll expand on it slightly…I spend probably 80% of my day either sleeping, sitting in front of the computer, or out walking around. Consequentially, the most comfortable and expensive things I own are my mattress, my office chair, and my shoes. Spend your money where it matters.