The Thirteenth House - Sharon Shinn

When the Romar Brendyn, the king's regent, is kidnapped, King Baryn sends his trusted band of mystics and warriors to retrieve him. It falls to Kirra, elder daughter of the house of Danalustrous, to contact him and describe the plan; the rescue is successful, and from the first moment she is strangely attracted to the dashing lord; that he is married affects her attraction not at all.

On her return home, marlord Malcolm gently informs Kirra that he will be naming his heir - and that he has chosen his younger daughter. Kirra's mother left when she was all but a babe, and contrary to expectation she is exceptionally close to her step-mother Jannis, and her half-sister Casserah. Kirra knows that Casserah is the better choice - her principal loyalty is to Danalustrous rather than Gillenagaria, she has no restless need to roam, and she is not a mystic. Kirra is relieved by the news, but needs some time away from home to fully absorb it.

Aware of the threat posed to the throne, King Baryn has decided that his heir, the reclusive Princess Amalie, will tour Gillengaria, alongside her step-mother, Queen Valri. As well as hopefully reassuring the people, he hopes to both garner information and demonstrate his power. It's the season for balls, which serves a perfect pretext, and Casserah would be a perfect companion, but for the fact that she abhors social outings. So Kirra shifts her form to that of her sister and, accompanied by fellow mystics Cammon and Senneth, her own faithful companion (and shape-shifter) Donnal, and Kings' Riders Justin and Tayse, the royal party tour the Twelve Houses of Gillengaria.
This densely plotted, seamlessly written combination of political intrigue, magic, religious zeal, reckless romance, love, passion, loyalty, heartbreak, power and sacrifice was a joy to read, marred only by my inability to put it down. The dialogue is convincing, the world building subtle and meticulous, the plotting deft and the scene setting evocative. This is a rich and luxurious novel that is perfect for total immersion. It's going to take an effort of will to prevent me gorging on the next novel... - Alex

The Twelve Houses series
1. Mystic and Rider
2. The Thirteenth House
3. Dark Moon Defender
4. Reader and Raelynx
5. Fortune and Fate