The Queen Saves the King (Camfield #89)

Pythia was aghast at her own daring. The diminutive young beauty had impulsively taken her cousin's place in a marriage decreed by Victoria herself! Now, settled in a distant land, the lovely imposter is determined to be a worthy Royal to her new subjects -- and a true consort to their dashing, cosmopolitan King. Wed in name only, Pythia had fallen in love with her husband... and vowed to win his errant heart. But just as they discovered the radiant promise of their union, deadly treachery flared. And Pythia must act boldly once more -- to foil a foreign monarch's plot -- and claim love's deep and enduring miracle!