Twelve houses, book 2: The Thirteenth house
Sharon Shinn2006

After joining an unlikely band of soldiers and sorcerers to rescue the kidnapped regent Romar Brendan, the shiftling Kirra returns home to learn that her half-sister, Casserah, has been proclaimed heir to the land. But when Casserah refuses to go on a social tour of great Houses, Kirra shifts into her sister's form and makes the rounds-during which she unexpectedly encounters her former compatriots. The motley group of mystics and warriors faces many dangers-and Kirra places herself in peril when she falls in love with the married Lord Romar. Revealing her true identity to him, Kirra begins a tempestuous affair that places them both in mortal danger, and leads them both into the stronghold of the devious lords of the Thirteenth House...