Five top "What If?" books

Karen Thompson Walker is author of the debut novel The Age of Miracles.

For The Daily Beast, she tagged her five favorite "What If?" books -- "books that envision our world having undergone a great change."

One title on her list:

Never Let Me Go
by Kazuo Ishiguro

Sad, lovely and layered, this book about young people doomed to brief lives is made all the more moving because of the restrained,