Can you identify this supernatural thriller?

This is a book that I read several years ago, but probably not more than five, and I think it was recent at the time. It was a library book, a hardcover, so it didn’t go straight to paperback.

I think it was by a well-known author. I can’t pull up a name, but I’m virtually certain it wasn’t Stephen King or Dean Koontz. It was the sort of thing that would be comfortable on the same shelf with their work.

The main character and, I think, his wife were both named Lee. The storyline involved a small group of students who fell under the spell of a charismatic leader. Under his influence they gathered to perform a peculiar ritual in a remote field. Spirits were summoned, something got out of control, and something terrible happened. The aftermath included some sort of tragedy and in one case madness.

The members of that little group were tracked down later in life by the main character, who discovered that the leader was still in touch with some of them. There was (I think) some sort of race against time at the climax, perhaps involving an ill-fated airplane flight.

Not only was it pretty spooky but it also included some interesting philosophical speculations on something that I thought was noteworthy at the time, even though I’ve forgotten it now.