[sufue]

I think Amy Corwin's Second Son Inquiry Agency books are probably self-pubbed (Fireside Mysteries?), but in any case, I've read and enjoyed all four of these historical mysteries. (They probably drift over into romantic suspense, but Corwin also writes some straight-up romance, and these aren't that, so I'm putting them here...)

Right now, the first book, The Vital Principle, is free at Kindle US and UK, though, so you can just try for yourself. And if you like it, the other three books are pretty reasonably priced all the time, so you don't have to spend a lot for them either. (And they are all KU, if you have a KU membership...)

Kindle US: https://www.amazon.com/dp/B004OR1GQ2
Kindle UK: https://www.amazon.co.uk/dp/B004OR1GQ2

Spoiler:

When Lord Crowley sends for him, cynical inquiry agent Knighton Gaunt is more than happy to accept the simple assignment. All he must do is attend a séance and expose the spiritualist, Prudence Barnard, as a charlatan taking advantage of Crowley's mother.

Unfortunately, instead of proving Miss Barnard is a fraud, Gaunt is made to look like a fool when Crowley is murdered after the séance. Apparently, the attractive spiritualist is not the only guest who has mastered the art of sleight-of-hand. Whoever killed Crowley managed to poison his brandy without anyone noticing and to act with appropriate concern afterwards.

The terrified guests immediately close ranks against Miss Barnard and accuse her of the murder. She is the only stranger in the house, except for Gaunt, and she'd argued with Crowley the previous day. It sounds reasonable to everyone except Miss Barnard. And Gaunt.

Then the murderer strikes again, and Gaunt must use all of his skill to expose the truth before another member of their house party dies.