With the Lightnings by David Drake
This is the first installment in the Republic of Cinnabar Navy series, which are essentially Master and Commander in space, and with 98% less early 19th-century naval jargon.
Lt. Daniel Leary is sent to accompany a diplomatic mission to Kostroma, which is a sort-of-neutral player in the game between Cinnabar and the Alliance. He meets Adele Mundy, a librarian-spy with a traumatic past.
There are diplomatic double- and triple-crosses, and Lt. Leary and his misfit band, including Adele, save the day.
Parts of it were kind of frustrating, like Leary's attitude toward, well, everyone who wasn't from Cinnabar or the navy, and his casual sexism. At the same time, these attitudes are very much like the ones Jack Aubrey displays in O'Brien's work, and because the RCN series is based on those, it makes sense.
Overall, it was an enjoyable read, full of diplomatic intrigue and space battles, snarky humor, and great characters.
The first three books are available in the Baen free library. The first six are available free here, along with a few other works by Drake.