Diplomatic Immunity, by my favorite SF writer - Lois McMaster Bujold. I find her books compulsively readable, and well worth re-reading. (The fact that she's won 5 Hugo awards and a Nebula award - for novels - doesn't hurt, either.) She has a writing style that asks "what's the worst thing that can happen to this character?" and then shows us how her character deals with or solves the situation - often growing or learning in the process. She doesn't skip the hard parts but writes through them, showing the details. Another aspect that I particularly like is the way her characters have an immediate response or reaction that they think but don't voice - often uncomplimentary (something we can recognize in ourselves.) As a Bujold fan I'll be happy to sell as many nice copies of her books as I can find.

[I'll start with the flap-copy from a hardcover, and expand on that for a plot summary/teaser...]
"A rich Komarran merchant fleet has been impounded at Graf Station, in distant Quaddiespace, after a bloody incident on the station docks involving a security officer from the convoy's Barrayaran military escort. Lord Miles Vorkosigan of Barrayar and his wife, Lady Ekaterin, have better things on their minds, such as getting home in time to attend the long-awaited birth of their first children. But when duty calls in the voice of Emperor Gregor, Miles, Gregor's youngest Imperial Auditor (a special high-level troubleshooter) has no choice but to answer. Waiting on Graf Station are diplomatic snarls, tangled loyalties, old friends, new enemies, racial tensions, mysterious disappearances, and a lethal secret with wider consequences than even Miles anticipates: a race with time for life against death in horrifying new forms. The downside of being a troubleshooter comes when trouble starts shooting back... "

[My comments]: The latest by internal chronology (as of 2002) of the books which feature Miles Vorkosigan, and Bujold expertly combines threads from earlier books or stories to bring results at this particular place and time. (If you think back to when he last encountered Quaddies, you'll have a good idea of who from his past will be here.) Miles continues to grow into his new role of Imperial Auditor, having to play the familiar role of detective to find out what actually happened (and why.) Miles is supposed to be past his action/adrenaline days, but somehow he ends up in situations where his old habits are needed - and continues to be adept at exploiting whatever clues or opportunities are presented. This one tends more toward the light/manic side of Bujold, but like any of her books, delivers satisfying moments and surprises.