IMHO, this is one of Miller's better books. The characters are all ring true, and the tale is told in an interesting way.
Summary, no spoilers:
Eva and Mark had two children, named Emily and Daisy. When the girls were small, Mark has an affair, and the marriage ends.
Eva remarries John ("a nice guy"), and has a son, Theo, with him.
When the book opens, we discover that John has been killed in a car accident (he was a pedestrian), and everyone is feeling enormous grief.
The book tells the story of that grief, and how each character deals with life without John.
Mark now becomes a more vital part of the family's life, Eva deals with loneliness, and Daisy, 14 years old and the most troubled, deals with her grief, her alienation from other kids, and her burgeoning sexuality.
This is a quick read. As usual, Miller is entertaining, and in particular, in this novel she has created a realistic group of characters.
The only reservation I have is with the ending of this book. Miller's last chapter takes place well after the events of the book, and it does resolve a lot of questions as to what happens to the various characters. It is just my opinion, but I would have preferred a different ending. It was a bit of a letdown for me, and I felt like I was meeting different characters than the ones I had come to know intimately throughout the novel.
Despite this, Lost in the Forest is a very good book, and I highly recommended it.