I just recently became aware of the Will Raven/Sarah Fisher historical series by author duo Ambrose Parry, so haven’t read any of the books, although they look quite interesting. It’s set in 1840s Edinburgh, with a medical background.
There is a novella in the series available for free right now, The Spendthrift and the Swallow. Info differs as to whether this is “book 3.5” or “book 5”, but either way it’s free, so I’m going to try it out, even though it may not be the best entry point to the series. And the other books (other than the most recent one) do seem to go on sale reasonably often, which is nice to know when trying a new series…