Annie, Mason, and Jake have been friends since childhood. From their lemonade stand to their post-high school trip to Morocco, the triumvirate has battled Mason's jealousy. Mason always wanted to be the center of attention and attraction; he wanted to be Annie's girlfriend AND Jake's best friend (and even more).
When Mason kills himself, he leaves Annie and their daughter, Opal to pick up the pieces. There's something Annie's done to precipitate the suicide, the worst thing she's done. And there's Jake. The worst thing he's done is also related to Mason's death. And, finally, we'll discover the worst things that Mason has done.
Hegi tells their story from multiple points of view, in both flashback and present tense. More than anything, the change in narrator keeps the novel flowing for the reader, who would otherwise be bored.
This is not one of Hegi's best novels. If you have never read her work, try Stones from the River or The Vision of Emma Blau. Both of those novels are superior to her current offering.