The narrator is an English teacher named Neil Countryman, who had a friend from high-school age named John William Barry. John William came from a very wealthy, if dysfunctional family.
Countryman and Barry shared a love for back country hiking. At one point, Barry arranges, with Countryman's help, to disappear into the Ho Rain Forest on the Olympic Peninsula.
According to the blurb on the CD case, there is a "revelation" near the end of the story, but I'm damned if I know what they mean. Perhaps this clip from the NYT review linked below covers it:
There’s a deus ex machina at the end of this new one that, a little disappointingly, plants guilt for John William’s struggles at the feet of a certain suspect. But the voice of Neil Countryman is that of a good, thoughtful man coming into middle-class, middle-aged fullness, and his recollections of life in Seattle have a wonderful richness and texture.
Set in Western Washington, as are other Guterson works, there is a lot of poetry in this book, but it does go on. And on.
New York Times review