The book is a parable about the Atonement. It is about a man who is having an argument with his wife. As he goes to bed, he remembers his late grandfather and thinks of how much he admires him. As he drifts off to sleep, his grandfather visits him and takes him back in time to witness firsthand certain events in the scriptures, explaining how those events teach about the Atonement. The events from the scriptures (mostly from the Old Testament) are ones that are not usually mentioned, so it is neat to see how everything is meant to teach about the Savior.
One of the things that I enjoyed the most about The Peacegiver is that the main character is believable. After having this wonderful experience, he is not perfect. In fact, after trying to apply the principles he learned, he fails and quickly returns to the "natural man." Even at the end of the book, the main character is not perfect, but has the determination to do better. I really like this because that is the case for all of us, especially for me. But no matter how many experiences I have with the Atonement, I always mess up and need the Atonement again. But that is the beauty of the Atonement: it is always there to help us up again.
Another thing I really love about this book is that it talks not only about how the Atonement helps the sinner, but also helps the person sinned against. It is wonderful that it is able to satisfy both sides. I highly recommend this book to anyone. It is very easy to read and understand, and I promise your heart will be touched by the Spirit.