The Night Circus by Erin Morgenstern isn't just a romance book, but it's that very blend of genres (and its incredible worldbuilding) that would make it such an amazing movie. At its heart, it's about the decades-spanning relationship between two magicians: Celia and Marco, raised from birth to do battle to the death in a proxy war between two ancient rivals. The venue for their years-long competition is a magical circus, filled with oddball people and beautiful but dangerous acts of magic. As they draw closer to the end of their deadly game, Celia and Marco's feelings for each other force them to try to find another way out, or else be separated forever.