Wow! I read 73% straight through in 2 hours and the rest in an hour...I need to go back and read her previous 2 books. 

Marcus and Sydney bump into each other one morning at Dunkin and decide to spend the day together and not go about their planned days. But then they get stuck in this day over and over again. 

They eventually come to realize that they might need to lean on each other as both are grieving. I think this day helps them feel worthy of being able to grieve. It helps them help each other. It's sort of amazing what breaks the cycle but also understandable. The ending is a little interesting but felt perfect the way it happened even when I might have expected another outcome.