Tracy Grant has written a very complicated historical series featuring first Charles and Mélanie Fraser, and then later Malcolm and Suzanne Rannoch, who are recognizably the same couple, but with different names, apparently due to some publisher disputes. And to make matters more confusing, probably due to the same dispute, some of the books were published using Tracy Grant and some using the pen name Teresa Grant. And finally, Grant didn’t write the early parts of the series in much of a chronological order. But, if you can wade through all of that, I’ve found it to be quite an enjoyable series, both the traditionally published and the later titles. You can find more info on recommended series order in the FAQ on Grant’s website.
Now here is The Carfax Intrigue, one of the more recent (2020) titles in the series, on sale in the US/UK for $0.99/£0.77. I haven’t read this one, but as I said above, I have read most of the titles in the series and have liked all that I have read.