Stay away. Seriously.
I don't care that it has a foreward by Kripke endorsing it, or that the writer is a worker on set who apparently doubled as a sounding board for the showrunners. It's not a good book. The story is contrived, the characterization is lacklustre and tacked on, and the research is poorly integrated.
I have a mild obsession with Danvers State Asylum and what's become of it. I love the Kirkbride buildings and the architecture of the place. I love the history of it and the way it just loomed up out of nowhere. I wished it had been declared a historical site rather than sold to developers, and it's a pity that it's now a total write off except for its history.
"One Year Gone" takes place at the old asylum towards the end of it, and a bit near the middle.
The overall plot is that Dean is looking for a way to break Sam out of the cage. Soulless Sam is following him for... Well, the reasoning doesn't really fit for what the show has displayed regarding that aspect of characterization. Under the pretence of a family vacation, Dean takes Lisa and Ben to Salem in search of a witch with the Necromicon.
So, in a book generally touted as a supplement to canon events, the audience is treated to:
-Sam's character wavering-- why would he care about Dean when Dean is neither useful at the moment, nor intimately connected with his own hunt?
-Dean-- not just having nightmares, being on edge, or instinctively hunting in a mundane setting-- knowingly puts Ben and Lisa in danger, after lying to them.
-Lisa went along with it and does nothing more than scolds Dean when the danger's over.
-Ben, being all of twelve that he is, goes on dates. Lisa allows him.
So, four main characters, four main fuck-ups.
Say what you want about her, when Lisa was actually fleshed out in the show, she had a backbone and was a protective mother. While she didn't understand hunting, or Dean's paranoia, she was completely normal. For fuck's sake, she told Dean to hit the road when he pushed Ben.
Ben, in the show, unfortunately was never really fleshed out. And in his early teen self, we don't get much of a look at him other than seeing that he idolized Dean, wanted to follow in his footsteps as a hunter (kid had a serious case of hero-worship), and was entirely normal.
This wandering off with a strange girl in an unknown city, with Lisa's permission? Bullshit.
Dean wouldn't have been kicking around the house if anything like the book had actually happened in canon. In the show, Dean had every appearance of trying to move on. He sucked at it, but he was trying.
But see, the characterization just made it painful. Never mind there's an instance where Dean parts with John's journal, or the tacked on family history of the Campbells. What made the book intolerable for me? The depiction of Danvers.
Yes, the asylum was known to have tunnels and "secret" passages for the staff to move between the wings and buildings during the winter. The tunnels are all well documented, as were their uses, and the staff rooms. While it's nice to think that, during renovations, the accesses would have remained open or worked directly into the residential design... No. Not going to happen and not logical. The book cast the building-- just the Kirkbride, too-- as the necessary "evil castle stronghold" for the witch's. They included the idea of insane ghosts, murderous ghosts, and so on. But... We've seen it all before.
Witch's were addressed in the series. If going by the books, "Witch's Canyon" had an excellent portrayal for a hunt. If by the show, you get the demon element manipulating human stupidity. This book had neither.
Now that the big reveal of the Campbell family is done with and worked in as often as possible, it seems that the book could only think to use them as a "your family fought them before" thing. Pulling up the Striga storyline from the early seasons-- but only the entire family is inept at this hunt, and it wasn't just John freaking out that his kids almost died. The clan gets worked in as much as time travel for a plot device.
At least this time they left Castiel out of it.
In short and spoiler free:
The book is bad. It's strung together with almost no narrative logic, it fails to maintain the characters in any sensible way, or restore the status quo to pre-season standards. And it's just bad. I literally cringed as I read it.
There's better fanfiction out there. And I can't believe they ruined all that history and potential! Danvers Asylum is one of the most atmospheric establishments I've ever seen. It's beautiful and creepy, and had so, so much potential. For fuck's sake, it inspired Lovecraft! Would it have been so hard to just draw on Lovecraft's style, pacing, or themes when tossing the Winchesters into a story about Danvers and the Necromicon?
... It may have pissed me off a bit.