Hidden Warrior - Lynn Flewelling

Lynn Flewelling's The Hidden Warrior is the second book in the Tamir Triad. At the start of the book Tobin wakes up after discovering that he is really a girl hidden in a boy's body by the magic of Lhel, a Hill Witch (whose magic is mostly despised as necromancy by the Oreska wizards). But this boy's body is the only body Tobin has known for the last twelve years and getting used to the idea that he is actually a girl will require time. Unfortunately there is hardly any time for Tobin to consider it, because Ki, his squire and best friend, is lying severely injured, possibly dying. No one seems to be able to tell Tobin exactly how Ki was injured. Then Tobin's horrible guardian, Lord Orun, keeps writing to Tobin, telling him to come back to Ero, because he wants Tobin back under his control. To add to his stress, King Erius, his uncle whom he's never met and only seen briefly once, is on his way back from the wars against the Plenimarans. Erius is the one who ordered the deaths of all the females of his line, and Erius is the reason Tobin is disguised as a boy. The final burden that Tobin bears is Brother, the demonic ghost of his dead twin brother, who seems to be gaining powers of his own.

Tobin eventually goes back to Ero; the capital city is increasingly beset by plagues, a consequence, so Iya, Arkoniel and other Illorians believe, of Erius' usurpation of the Skalan throne. Despite the Harriers, the band of wizards loyal to Erius and his chief wizard Niryn, who are desperate to control wizards such as Iya and other Illorians, the old magics are not only being preserved, but the wizards are aware of Iya's vision of a queen on the throne of Skala, even though they know nothing of Tobin.

Every now and again Tobin remembers that "he" is destined to be Queen, but this is not a comfortable thought, because he loves Korin, his cousin, who is heir to the throne, and he discovers that he even loves the king although sometimes the king's rages are difficult to survive. Then Ero, which is already stricken by plague, is attacked by the Plenimarans - and for Tobin, events take on a avalanche-like quality.