An interesting book. Not, as you might expect, full of new spells and prestige classes but instead it takes a softer, more fluff/less crunch look at magic specific to the Land of the Diamond Throne.
New rules subsystems are introduced in the form of ceremonies, very similar to Mike Mearls' other subsytems in Legacy of the Dragons for Charm Sets and Rune Manifests (the latter of which are expanded here). Simply, you get a minor spell-like effect for a bit of cash but all three systems include a helping of flavour text.
There are some new Runes (for Runethanes), a few new spells, some variant RuneChildren (based along specific lines such as magic, combat or stealth) and a sort of Anti-RuneChild.
All in all it's quite a nice book - a lot lower key than you might expect with the emphasis on magic being this all-pervasive subtle thing that every one uses a little, rather than the more typical "bigger spells to blow up bigger things" kind of power-up book (although there are some flash-bang 9th level spells).