Inside, inside shells;
a game of princes. Princess?
Agent. & ship? Knight.
Well, I sure do like these Culture novels. This one is "out of order" though since the books aren't a series so much as an idea, it doesn't matter. The story follows three plotlines, each attached to the member of a barbarian aristocrat family. I say barbarian-- I mean that pretty deeply. In Matter the "tiers" of galactic advancement really come into play-- the main nation in question has been kick-started into the Industrial Age by a rogue Culture agent; they are in a nestled (Russian doll-like) layer of a world made of shells & shells. Controlling their layer-- or really more importantly, the elevators between layers-- are the Oct, a "sci-fi" race of crab-men. Controlling the giant shellworld are the more advanced Nariscene, bug people. Now, controlling the area of space that the shellworld is in are the Morthanveld, a sea-urchin-type alien species that is more or less on the same technological footing as the Culture. The Culture aren't even in play, except in that they directly effect the story by dint of one of the characters.
The king is dead! Well, skullduggery is afoot, which Ferbian the hapless prince & Oramen the studious prince need to deal with. Ferbian takes off to go find help from some aliens. Oramen is left Prince Regent. Those two storylines take up a nice two-thirds of the book, making a great deal of it read like a fantasy novel, complete with flying mounts (gravity being about half Earth norm) & knights & all that. The third sibling is Djan Seriy; her father the king "married" her off to the Culture. Well, really the Culture offered her the chance to go & she took it; the savages just didn't know how to understand it. Since then she's gone Special Circumstances, & she is coming home to grieve for her father's death, or at least so she supposes.
There is a lot of non-Culture science-fiction here, which fleshes out the galactic stage a little; of course, Banks will probably never return to it, or at most will make a nod in its direction. You've got to admire than Iain Banks understands vast numbers involved in time & space (or at least, understands them a little; I'm not sure anyone can properly understand anything in the trillions). Things in the Culture novels happen thousands of years apart, millions of lightyears away from each other. Space is really, really big. The book is a tome at six hundred some pages, & nicely appendiced. I didn't need it, since I blazed through the book in a few days, but it might be comforting to know up front that there is a Dramatis Personae & glossary lurking in the back. For all that, context clues are strong; you don't need to scurry about back & forth, except maybe to your notebook.