Barrett Bloom is hoping college will be a fresh start after a messy high school experience. But when school begins on September 21st, everything goes wrong. She's humiliated by the know-it-all in her physics class, she botches her interview for the college paper, and at a party that night, she accidentally sets a frat on fire. She panics and flees, and when she realizes her roommate locked her out of their dorm, she falls asleep in the common room.

The next morning, Barrett's perplexed to find herself back in her dorm room bed, no longer smelling of ashes and crushed dreams. It's September 21st. Again. And after a confrontation with Miles, the guy from Physics 101, she learns she's not alone--he's been trapped for months.

When her attempts to fix her timeline fail, she agrees to work with Miles to find a way out. Soon they're exploring the mysterious underbelly of the university and going on wild, romantic adventures. As they start falling for each other, they face the universe's biggest unanswered question yet: what happens to their relationship if they finally make it to tomorrow?