The best way to learn the plot of this excellent novel is to read it for yourself.  If you haven't already, I highly recommend it.  If you are looking for a basic plot summary to determine whether or not you want to read it, I can help you there.  Enotes also provides great resources for anyone who is curious about the contents of a book-they have summaries and discussions of most novels and books out there. I have provided a link below if you want to take a look at it.

"Peace Like a River," written by Leif Enger, is about a family, two brothers and a sister, whose mother left them when they were small, so their father had the responsibility of raising them.  They live in North Dakota, and their father is an interesting man, who can perform miracles, and has a distinct and unique relationship with his faith and God.  The little sister is bullied by some very creepy boys at school, who threaten to harm her physically, and assault her.  The oldest brother, in an attempt to protect her, ends up killing one of them, and then goes on the run in order to evade arrest.  Their family sets out on a road trip to try to track him down.

The strength of this novel is in the characters--they are very well-written, and seem like truly real people.  They are very endearing, and work their way into your heart.  The conflicts presented, on whether to help their brother or not, provide an interesting dilemma that gives plenty of thought-provoking discussion.  As the family tracks down their beloved brother and son, they run across people that help them, people that want to harm them, and plenty of miracles that aid them in their journey.  I hope that those thoughts helped; good luck!