Cybele's Secret - Juliet Marillier

For Paula, accompanying her merchant father on a trading voyage to Istanbul is a dream come true, and even better, he is allowing her to act as his assistant. They have come to this city of trade on a special mission to purchase a most rare artifact, a gift from the ancient goddess, Cybele, to her followers. It's the only remnant of a lost pagan cult. But it soon becomes clear they are playing at a dangerous game. A colleague of Paula's father is found murdered. There are rumors of Cybele's cult reviving within the very walls of Istanbul. And most telling of all, signs have begun to appear to Paula; signs that can only be coming from the mystical Other Kingdom, urging her to unlock Cybele's secret. Paula doesn't know who in Istanbul she can trust and finds herself drawn to two very different men: a mysterious, dashing pirate and her bodyguard, Stoyan. As time begins to run out, Paula realizes they may all be tied up in the destiny of Cybele's Gift, and she must solve the puzzle before unknown but deadly enemies catch up to her.