This is a Robin Cook book. Usually his books follow a fairly predictible pattern. Young idealistic doctor discovers some kind of horrible corruption or evil conspiracy and must expose it. And of course he must do so all on his own and is hunted by the Bad Guys the whole time, the authorities never believe him... but eventually he succedes and takes down the Big Evil Corporation. I do enjoy his books, it's just that I know what to expect from them.
This one didn't follow that formula at all. And I quite enjoyed that!
I have no idea how much of it is based in actual research of the history or how much of it is possible, but there's a lot of really interesting stuff in this one about the Salem witch trials and what could have caused them. Since the cause being actual witches seems a little far-fetched.
He also touches on psychopharmacology and how much of our personalities are we willing to change with drugs. How much should we change?