In What World by Bridget Morrissey

Two high school rivals begrudgingly reunite as adults to investigate the disappearance of their beloved former teacher, only to wind up traveling through a series of alternate realities together.

Total opposites, Marlowe Jenkins and Priscilla Covington-French hated each other in high school. Now in their thirties, Marlowe is barely scraping by while Priscilla is wildly successful. Their rivalry should be long dead, yet both women remain connected through their mutual mentor, drama teacher Dallas Winthrop. Their unending tension has nothing to do with the fact that they’ve kissed. More than once.

When Dallas goes missing, each woman believes she can figure out where he is. Except this is no ordinary disappearance. Dallas has found a way to explore alternate versions of reality. While trying to follow him, Marlowe and Priscilla find other versions of themselves instead, surprised to learn not all Marlowes and Priscillas are fueled by hate. In fact, some Marlowes and Priscillas have very different strong feelings for one another. . .

The more Marlowe and Priscilla are forced to rely on each other, the harder it becomes to ignore their simmering attraction. But with every alternate reality they search, they only get further from their real life and responsibilities. Do they play it safe and hide behind their rivalry, or take a chance on each other that could permanently change the world as they know it?