King of Wands by Amy Kuivalainen

Things are finally going right for Ezra. She’s living in Florence, and her skill with rare sigil magic is unbeatable. Everything was going fine…right up until a crazy cabal of magicians decide to drag her back to Venice. Not only is her new captors determined to sell golem soldiers to the Varangians, they want Ezra’s magic to make it happen.
To save herself, Ezra will have to swallow her own prejudices and go to the one person in Venice that could help her; The Djinn King of Wands, Zahir Matani.
Zahir knows how to get the most from a deal. Sure, he’ll help Ezra, but only once she’s exposed the Republic’s enemies and fulfilled the small caveat that she has to spend three nights with the djinn king at a time and place of his choosing.
It’s better to make a deal with the Devil than a djinn, and Ezra has never met a man as ruthless as Zahir. He might be wiling to save her from her captors, but who is going to save her from him?