The plot (without giving away spoilers): the Dowager Empress of Cetaganda has died, and Miles Vorkosigan and his cousin Ivan are despatched to attend the funereal ceremonies - as representatives of the Cetagandans heriditary enemies, the Barrayarans. Immediately upon arrival they are handed a mysterious artefact by someone who is murdered, soon after - and trouble ensues. Not just ordinary trouble (which seems to accompany Miles wherever he goes) but interplanetary trouble... multiple and dangerous cross-currents, plots and unexpected, um... relationships abound. The Barrayaran Ambassador gets more than normally exasparated with his two young trainee diplomats!
My opinion: hugely enjoyable, and superior to most other SF or space opera that I know - in that it is smart, complicated and fallking into place(s) in a *very* satisfactory way, exasparating, tense, moving. Very well-plotted, with delicious writing and fully-fledged 3-D people inhabiting a convincing, and fascinating, universe. Bujold has a knack of springing shock surprises on you (and her protagonists) that leave you reeling, mentally, and soon thereafter nodding your head at the convoluted logic of it all. Terrific stuff, and hugely enjoyable, in the way of Modesty Blaise, say, with a dash of Vance, Heinlein and Leiber. Anybody who doesn't know the Vorkosigan series should start at the beginning ('Shards of honor') and work their way through; anybody who knows Miles will find him in full flight and top form.