Everybody's got a number. In fact, everyone has a few numbers. There's the one we tell our friends, the one we tell our boyfriends, and the one, if absolutely pushed, that we tell our parents. But only we know what our true number is. Well, I was getting a little self-conscious about my number. So I decided that twenty would be my limit. No more. Not ever. Delilah Darling wakes up one morning to realise that she has, without meaning to, hit the big twenty and she still hasn't found the one. She has only one option - to go on the ultimate road trip back to the beginning and revisit all those past lovers. Could she have missed the love of her life without realising it?