I thoroughly enjoyed this. At midnight one night Haig's protagonist finds herself in a huge library, where she can step into any of the lives she might have lived if she had made different choices (stayed in the band, said yes to the coffee date etc) Predictably, through all this, she finds that in each life, there she herself is, she can't ever escape that, but she comes to realise what she does actually want out of life.
There are a few details I'd change about the book and I think there could have been less time on the big, obvious regrets and more on the little ones, or more on the fall-out of having to leave these other lives when she wasn't totally happy there. However in the end it was a great book, compellingly written and with a nice ending