Very quickly, she realizes that she's not alone in this loop in space and time. Miles, her neighbor in physics, is also stuck in the loop. And while he's rude and arrogant, she concedes that she needs his help (and he comes to the conclusion that he'll tolerate hers). Their lives become an exploration of how they are going to escape from this one day cycle to the magic of tomorrow.
The obvious inspiration is the Bill Murray comedy Groundhog Day and this is basically the latest in a long series of YA stories about being stuck in a day that continually repeats. I particularly enjoyed this one for three reasons. First of all, it acknowledges the debt. Even the characters are familiar with the film (they actually watch it at one point) and they try out a few of the ideas from the movie. Secondly, the book makes some attempt to explain why the loop is happening. It's pseudo science, but it puts in the effort and doesn't just rely on "magic" or "fate." That gives the story a sense of adventure that is lacking in most renditions of this trope that I have read. Finally, Solomon is just a delightful writer and the story just whizzes by. It's a fun read.