Next week, Intrepid Shakespeare Company will stage an adaptation of Henry James' novella The Turn of the Screw, hailed by many as one of the, if not the, greatest ghost stories of all time.

Seemed so to me the first time I read it - alone in a log cabin in the Santa Cruz mountains, on a night both dark and stormy. I swore I saw Peter Quint and Miss Jessel's rain-drizzled faces on the window and in the smoke curling from the rock fireplace. Sometimes just their unblinking eyes, big as baseballs.

Quint and Jessel are - or, many contend, are not - the ghosts of former servants haunting a young governess and two children at Bly, a country estate.

Two questions haunt me still. Are the ghosts in the story real - can the children see them? - or is the governess just hallucinating? And did Henry James believe in ghosts?

James is gleefully evasive about the story. He's called everything from a "fairy tale" to a "wanton little tale" to "a rather shameless potboiler."

He does say, albeit cryptically, he admires the craft: how it sustains the mystery in the reader's mind throughout. "So long as the events are veiled the imagination will run riot and depict all sorts of horrors, but as soon as the veil is lifted, all mystery disappears, and with it the sense of terror."

(the novelist Graham Greene admired James' coy treatment: "at a certain level, no writer has really disclosed less").

So James' makes contradictory remarks by design: to keep the story ambiguous - and still vital.

But was he a believer? Gets tricky here too.

In his youth, James poo-pooh'd seances ("spirit-rapping") and "ghost-raising." But possibly inspired by his brother William, he developed an ongoing interest in the unconscious and "the other side."

William James was one of America's most influential thinkers. He wrote The Varieties of Religious Experience, The Principals of Psychology and Pragmatism.

He was also one of America's most ardent students of the supernatural, and risked his professional career pursuing non-scientific subjects. He co-founded the Society for Psychical Research and - a relentless seeker of first-hand experience - went to hundreds of seances.

These used to be called "ghost evenings." The Turn of the Screw begins with one. William debunked most of them, often on the spot. But some convinced him to "remain uncertain and await more fact."

(Fascinating book: Deborah Blum, Ghost Hunters: William James and the Search for Scientific Proof of Life After Death. When members of the PSR died, several came back in seances and complained that spirit mediums are inept and need much better training).

Henry James always kept an eye on his brother's findings. When William died in 1910, Henry and William's wife Alice went to several ghost evenings in Boston to make contact. None did, and Henry - revealing his true feelings on the subject? - attributed the silence to "the grim refusal of the dead."

Just days after Henry and Alice's last one, the New York Times reported that William had spoken from the spirit world. "I am at peace," he said. "I have awakened to a life far beyond my highest conception while a denizen of the earth." The voice, which echoed William's style, promised to contact Henry soon.

If it happened, Henry never said.