Amazing book - fascinating, well-written, and surprisingly not that depressing. I'm going to quote from the introduction here, since it does a better job of explaining what the book is about than I could.
"All across the nation we have snapped plates of armor onto our professional lifesavers. In return, we have very high expectations for these brave men and women. Only after everything goes wrong do we realize we're on our own. And the bigger the disaster, the longer we will be on our own. No fire department can be everywhere at once, no matter how good their gear."
"This book goes inside the black box and stays there. The Unthinkable is not a book about disaster recovery; it's about what happens in the midst -- before the police and firefighters arrive, before reporters show up in their rain slickers, before a structure is imposed on the loss. This is a book about the survival arc we all must travel to get from danger to safety."