Z for Zachariah

This book is  about a girl who is living in a valley after a nuclear war. One day she sees a fire near the hill that leads to her valley. Her valley is a nuclear free zone since it is surrounded by hills and mountains not allowing nuclear air in. Three days after seeing the smoke a person in a green suit comes over the valley. She can not see his face because of his mask. She hides up on the hills watching him. Is he good or is he a crazy man who barely survived? Find out by reading the book.