"This is the way the world ends" Part 1

There has been a chemical or nuclear war and 16 year old Ann Burden has watched her entire family sicken and die. The nearby towns are empty. Ann fears that she may be the last person left on earth. Then, one morning, everything changes. As Ann tells us: "I am afraid. Someone is coming. That is, I think someone is coming and I pray that I am wrong. I went into the church and prayed all morning. I sprinkled water in front of the altar, and put some flowers on it, violets and dogwood. But there is smoke. Not like the time before. That time, last year, it rose in a great cloud a long way away. But this time it is a thin column, not very high.... And it's moving closer each day." Ann is right: someone is coming. Will he be a friend, or an enemy? Is there something worse than being the last person on Earth?
Z for Zachariah by Robert C. O'Brien