There was a great deal
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I don't think the lack of an answer in the book hurts it. Instead, I think it probably helped it because all sides of the issue are thoroughly explained and explored. If the mystery had been solved prior to the book's publication, I feel like it would have been very easy to gloss over the groups and people who weren't responsible for the arson. Even though they weren't the ones burning down Vail's buildings, they still had plenty of reasons why they might like to see the new lodges gone.
The quote on the top of the cover is from Outside Magazine. They call Powder Burn "an alpine Midnight in the Garden of Good and Evil." I think this is an accurate description. Powder Burn gives a great feel for Vail as well as diving into the tension surrounding the ski resort and the fires. It only has a handful of reviews on goodreads, which to me is disappointing because it's a great read.