The Book of Tomorrow by Cecelia Ahern

This is a story about how tomorrow can change what happens today...
Tamara Goodwin has everything she ever wanted and she never has to think about tomorrow. But suddenly her world is turned upside down and she has to leave her glamorous city life for a new one in the country. However, Tamara is soon lonely and longing to return home.
Then a travelling library arrives in the village, bringing with it a mysterious leather-bound book locked with a gold clasp and padlock. What Tamara discovers within its pages takes her breath away and everything starts to change in the most unexpected of ways...