In this time shifting novel the two main characters, Helena and Barry, meet and re-meet under varying and mostly frightening circumstances in different timelines. Deaths happen and then unhappen. It took quite a while for the premise to become fully obvious and the book went downhill at that point. The plot became so preposterous and irritatingly repetitive that I skimmed and skipped liberally through the second half. So much of sci-fi literature is really just fantasy or pseudo-science and this book, unfortunately, falls into that category.