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.
Vienna Waltz is the third, chronologically, in Grant’s Rannoch/Fraser series. It has dropped to $2.99 at Kindle US: https://www.amazon.com/dp/B004IWR3L0
His Spanish Bride (not to be confused with Georgette Heyer’s The Spanish Bride) is the first title in this series, chronologically. It’s a long novella, and it has dropped to $0.99 at Kindle US: https://www.amazon.com/dp/B008R9VPUU
The Paris Affair is more-or-less the fifth Rannoch title, depending on who’s counting and how! It’s $1.99 right now in the US, and it’s discountable at Kobo US.
Kindle US: https://www.amazon.com/dp/B00ADQHGE4
Kobo US: https://www.kobo.com/us/en/ebook/the-paris-affair-7
The Berkeley Square Affair is the eighth Rannoch title. It’s $1.99 at Kindle and Kobo US, and discountable at Kobo.
Kindle US: https://www.amazon.com/dp/B00FH1IBUS
Kobo US: https://www.kobo.com/us/en/ebook/the-berkeley-square-affair-3
The Paris Plot, not to be confused with The Paris Affair, which is also a title in the Rannoch/Fraser series, is on sale right now at Kindle US for $0.99, and it’s also long-term at £1.99 at Kindle UK.
Kindle US: https://www.amazon.com/dp/B00F8J6O80
Kindle UK: https://www.amazon.co.uk/dp/B011LOZBUC
The Paris Affair is $1.99 again right now at Kindle US, but not on sale this time at Kobo US. The link in the comment about three above is still good…