Pretense and Poison — Amberlyn Holland

As official emissary of the dragon-shifter Sea Clan, Tomas is ostensibly in Ardell to celebrate his brother's betrothal to the kingdom's crown princess and negotiate a new treaty.  As unofficial spymaster, he's there to retrieve treacherous magic before it could be used against the dragons of his clan. Lady Alisandra flits through ballrooms and salons as naïve and carefree as any other noble-born daughter of Ardell. But a sacred oath leads her to more dangerous pursuits when no one is watching. When Alisandra and Tomas break into Ardell's royal vault on the same night, they find themselves thrown together on a strange quest filled with ancient secrets, renegade dark fey, and unimaginable danger. But will family duty and unbreakable vows end their new partnership before it truly begins?