An original novel based on the tv show supernatural, about two brothers who hunt monsters across america. As ever with tie in fiction it tells a story that is all new and hasn't been seen on screen. This one is set during the middle of the fifth season of the tv show.
Sam and Dean, at the behest of their friend and ally the angel Castiel, head for San Francisco to deal with the heart of the dragon, a force behind a series of murders, and one that reappears every twenty years.
Thus their father fought in previously in 1989, and their grandfather did the same in 1969.
The book thus tells us the stories of both those encounters.
And there's also a prologue set in feudal japan which fills you in on the origin of the force.
It runs for three hundred and ten pages. Afer the prologue, the first third of the book details the 1969 hunt, and the next third details the 1989 one.
Whilst all this is very interesting because of the back story it fills in for characters we didn't see too much of on tv, it means that there's not as much page time for Sam and Dean as you might like. They only come into the action with a third of the book to go. And whilst the tv characters are accurately depicted by the writer, and the supporting characters of his own that he comes up with are well written and believable and three dimensional in their motivations, the force isn't quite the most interesting adversary the Winchesters have ever faced.
The way it ties everything into the continuity of the show and the ongoing story arcs is very good, but ultimately whilst this is a decent piece of writing it's not a great one and perhaps not quite as good as it could be. For fans looking to fill in some of the back story it should more than suffice though, and it passes the time easily enough whilst waiting for the next new tv episode.