Caraval by Stephanie Garber

Scarlett has been writing to Legend every year for the past 7 years, but this year, she finally got the letter right. Legend is the master of Caraval, a magical, mysterious game where the winner's get fame, glory, and, this time, a wish. Scarlett and her sister Tella have been invited to Caraval, but Scarlett is about to marry a Count and finally take her sister away from their tiny island and their abusive father. If she leaves to play the game, she could ruin everything.