Just One Day

Just One Day - Gayle Forman

Just One Day is about a girl named Allison that goes to Paris with a organised group.  One day she breaks off from the group and finds the love of her life, William.  They spend a day exploring Paris together. The next morning when Allison wakes up William is not there. She leaves Paris in a sad state of mind. A year goes by and Allison decides she wants to go back to Paris to find him.