Bertie and Kate have been inspearable since high school. Now, Kate has recently decided to move from San Francisco to Los Angeles. When Bertie's attempts to make Kate stay fail, she suggests the next-best thing: a trip to Paris that will hopefully distract the duo from their upcoming separation. But once in Paris, they are caught up in a day that keeps repeating itself. In order to make her way back to Kate, Bertie has to figure out how much control she has over her future - and her past - and how to survive an apocalypse when the world keeps refusing to end.