The "Sapphire Rose", of course, is the Bhelliom, an object of such enormous power that worlds literally revolve around it and Gods have fought wars for it. All Sparhawk cares about, though, is that it is the one thing that can save the life of his poisoned Queen, Ehlana.
Ehlana's healed pretty early in, which leaves the rest of the book for Sparhawk to vanquish evil, destroy the Bad Guys, etc etc. See, once the Bhelliom resurfaces, Azash, the evil God of the Zemochs, knows who's got it. Since Bhelliom is the one thing Azash needs to free himself from his prison and take over the world, he's a little interested in getting Sparhawk to give it to him - or wresting it from his cold, dead hands, whichever's easiest. To that extent, there's a long, protracted section of the book devoted to the election of the Archprelate (the equivalent of the Pope) in the Holy City. If Annias, who secretly worships Azash, can buy enough votes, he wins, and Azash gets Bhelliom. So before Sparhawk can go off and kick immortal butt, he and his buddies have to head off this impending disaster first. It's political, it's complicated, and there are long sections where nothing happens but debate and voting. But it's also intelligent, witty, and gives several characters (including Ehlana) a chance to shine. Put it this way - if you think the political stuff in "Star Wars" is too complicated, you'll hate this part of the book. But if you enjoy that stuff, as I do, and seeing how wars are won by more than sword-waving, this book is fantastic.
Of course, there's real action, too - Sparhawk does face down Azash, with some help (of course). Ehlana and Sparhawk get married - their love story is both awkward and romantic, and quite cute. And someone dies - I can't say who, but I cried when I read it. (And there's no "Man-with-two-lives" business as in the Belgariad.)
The best book in a great series!