Shadow Study by Maria V Snyder
"Once, only her own life hung in the balance... Oddly enough, when Yelena was a poison taster, her life was simpler. But she'd survived to become a vital part of the balance of power between rival countries Ixia and Sitia. Now she uses her magic to keep the peace in both lands-and protect her relationship with Valek. Suddenly, though, they are beset on all sides by those vying for power through politics and intrigue. Valek's job and his life are in danger. As Yelena tries to uncover the scope of these plots, she faces a new challenge: her magic is blocked. She must keep that a secret-or her enemies will discover just how vulnerable she really is-while searching for who or what is responsible for neutralizing her powers. Yes, the days of tasting poisons were much simpler. And certainly not as dangerous..."
Snyder states in the afterword that she was done with the series but fans kept asking her for another book so she wrote this one. I think her lack of enthusiasm shows in this book which really doesn't add anything to the series. I did enjoy learning Valek's back story but we didn't really move much plotwise.