The third book Bone Key takes place in Florida where Dean and Sam chase down a sudden surge in supernatural activity. Ghosts and demons are running amok and an ancient force is rearing its evil head.
The fourth book Heart of the Dragon is set in season 5 with the apocalypse approaching and the demons and angels getting ready for the big battle. A demon ensnares a hero's soul and use him as deadly weapon in San Francisco.
For some obscure reason I never got around to reviewing book 3 after reading it and as such my memory about it is rather foggy. Like the previous two books it reads just like an episode of the TV show, but this time like a slightly poor one (hey, they can't always be fantastic). I may be wrong on this but I think I recall feeling Dean was a bit out of character.
Book 4 turned out to be downright disappointing. As a book in it's own right, the plot is not horrible - but Sam and Dean are barely in it! Something like half or even two-thirds of the book is set in 1969 and 1989 with their grandfather and dad being the lead hunters. S&D basically just turn up for the final few chapters and end it.