The book covers the period immediately after the accident to several months out, as the young man (Frank) comes to terms with what he's done and what's left for him to do in the future. His voice is authentic and anguished, and very believable. Aronson perfectly captures both the character and the voice, and does so without relying on a lot of physical movement (obviously) which is no mean feat for a debut novelist, as she was when she wrote this book.
We also see the way Frank's friends and the society around him react to what he's done - the divisions of opinion as to whether he's been punished enough for the wrongs he's committed or whether he deserves worse (death, a prison sentence etc). Aronson uses the narrative technique of having the characters comment on a website where people share (often heated) views about Frank and the accident. This reflects the varying attitudes in the town, even though the bulk of the story is closely told from the narrator's perspective.
The ending was moving and was the perfect conclusion to the story, even though some aspects of it were a little predictable. But that didn't matter because it wasn't the point of the book to have a "surprise" ending, but rather to illustrate teen and societal attitudes to issues like driving and drinking, and thinking you're invincible when you're not. The dialogue, emotion, and set-up are incredibly rich, but also extremely accessible. From the first line, the writing draws in the reader and doesn't let go. Beautiful and lyrical, yet raw and authentic at the same time. Really wonderful writing.