Someone Else's Shoes by Jojo Moyes
One day at the gym, Sam picks up a bag that she thinks is hers, but it isn't. In it is a Chanel jacket and Louboutins. She ends up wearing the items and having an amazing day at work. That same day, Nisha grabs a bag she thought was hers, and it wasn't. It had peasant shoes in it, if you will. A little later, Nisha's husband tells her he wants a divorce and cuts her off literally everywhere. Her husband has made it clear that in order for her to get any kind of divorce settlement, she has to bring him the shoes. What happens next is a series of events to get the shoes back.
Nisha is able to track down Sam, and they end up friends. There is so much more to this story, but I am afraid to share too much lest I give it away. Suffice it to say, Moyes has written another fantastic book, and this one is very much worth your time.