A page turner but a great pity that her editor or publisher did not check out the genetics underlying this story. The X chromosome problem as described by the author would not mean that only men would be affected by a virus. She needed to consider the Y chromosome instead. Her utter lack of knowledge shows when she uses two sets of twins - one identical and one fraternal -and their fathers to 'prove' the X chromosome is where the problem lies. Men don't receive an X from their father but from their mother. Once I'd read this part of the book, it soured the whole tale for me. I hope any film that results from this book corrects the genetic misunderstandings in it.