Planet der blauen Blumen

If I were the type of person to yell "Mary Sue," this book would have me yelling it. We learn of a wing of Starfleet that does investigations and is really rather gestapo-like; the lead character, Elizabeth, is investigating a series of deaths as the crew and a cargo of Federation ambassadors goes to try and, perhaps, negotiate a detente with the Romulans. Not great, but not great largely in that it reads very much like an actual original series episode that's been perspective-shifted onto the female love interest, so I can't hate it.

A bit of a murder mystery but not a great one.
The main investigator was not overly well written. Built up as being a complete hard-ass from the particular agency with augmented skills that can't be talked about. But then proceeds to be perfectly ordinary and friendly and vulnerable and falls into a tantrum when the stress of the answer just falling into her lap doesn't seem to occur. Does not appear to have any special investigative skills at all.
James Kirk portrayed as a very shallow womaniser but somehow this investigator falls completely for him and seriously considers a marriage proposal. This romantic development was a bit cringeworthy how it developed.
I also found it reasonably predictable how it would mostly go.

A fairly original "whodunit" murder mystery, in which an apparent "angel of death" is one by one murdering the ambassadors during a Federation diplomatic mission. A good mystery story, coupled with an original array of alien ambassadors, and for once a mature and serious love relationship developing between Kirk and the Federation investigating officer.