Journalist Tom Crane, researching a series of articles on the occult, gets drawn into the mysterious Department Seven and a deadly power struggle with a dangerous and charismatic man who shows him that all is not what it seems - not even Tom himself.
I read this as a kid, and loved it. On a re-read, it shows its 32 year age, particularly whenever computers are mentioned, and the writing isn't the most elegant I've ever read. But I can see why I loved it, and why it had such a formative effect on my tastes. Not as good as my memory might have wanted to make me believe, but still a very enjoyable, effectively creepy psi-thriller.