"You're quiet," Langdon said, gazing across the Hawker's cabin at Sophie.

"Just tired," she replied. "And the poem. I don't know."

Sophie squirmed in her seat. "I haven't told you what drove us apart."

Langdon was feeling the same way. The hum of the engines and the gentle rocking of the plane were hypnotic, and his head still throbbed where he'd been hit by the monk. Teabing was still in the back of the plane, and Langdon decided to take advantage of the moment alone with Sophie to tell her something that had been on his mind. "I think I know part of the reason why your grandfather conspired to put us together. I think there's something he wanted me to explain to you."

"The history of the Holy Grail and Mary Magdalene isn't enough?"

Langdon felt uncertain how to proceed. "The rift between you. The reason you haven't spoken to him in ten years. I think maybe he was hoping I could somehow make that right by explaining what drove you apart."

Langdon eyed her carefully. "You witnessed a sex rite. Didn't you?"

After a beat, she nodded.

"Were both men and women present?"

"Was it in the spring?" Langdon asked. "Sometime around the equinox? Mid-March?"

Sophie recoiled. "How do you know that?"

Langdon strained to hide his emotion, and yet he could not believe what he was hearing. Sophie Neveu had unwittingly witnessed a two-thousand-year-old sacred ceremony. "Masks?" he asked, keeping his voice calm. "Androgynous masks?"

"I'd rather not." She turned suddenly back to Langdon, her eyes welling with emotion. "I don't know what I saw."

Sophie looked out the window. "I was on spring break from university. I came home a few days early."

"Sophie, you told me you witnessed something that convinced you your grandfather was in a secret society. And whatever you saw upset you enough that you haven't spoken to him since. I know a fair amount about secret societies. It doesn't take the brains of Da Vinci to guess what you saw."

Sophie stared.

"You want to tell me about it?"

"Dressed in white and black?" She wiped her eyes and then nodded, seeming to open up a little. "The women were in white gossamer gowns… with golden shoes. They held golden orbs. The men wore black tunics and black shoes."

Langdon had read descriptions of this ceremony and understood its mystic roots. "It's called Hieros Gamos," he said softly. "It dates back more than two thousand years. Egyptian priests and priestesses performed it regularly to celebrate the reproductive power of the female," He paused, leaning toward her. "And if you witnessed Hieros Gamos without being properly prepared to understand its meaning, I imagine it would be pretty shocking."

"The ritual I saw was no marriage."

Sophie said nothing.

"Marriage as in union, Sophie."

"No?" she said, her olive eyes testing him.

"Yes. Everyone. Identical masks. White on the women. Black on the men."

"You mean as in sex."

"Hieros Gamos is Greek," he continued. "It means sacred marriage."

"No."

Langdon backpedaled. "Well… yes, in a manner of speaking, but not as we understand it today."He explained that although what she saw probably looked like a sex ritual, Hieros Gamos had nothing to do with eroticism. It was a spiritual act. Historically, intercourse was the act through which male and female experienced God. The ancients believed that the male was spiritually incomplete until he had carnal knowledge of the sacred feminine. Physical union with the female remained the sole means through which man could become spiritually complete and ultimately achieve gnosis -- knowledge of the divine. Since the days of Isis, sex rites had been considered man's only bridge from earth to heaven.

"By communing with woman," Langdon said, "man could achieve a climactic instant when his mind went totally blank and he could see God."

Langdon gave a noncommittal shrug, although Sophie was essentially correct. Physiologically speaking, the male climax was accompanied by a split second entirely devoid of thought. A brief mental vacuum. A moment of clarity during which God could be glimpsed. Meditation gurus achieved similar states of thoughtlessness without sex and often described Nirvana as a never-ending spiritual orgasm.

Sophie looked skeptical. "Orgasm as prayer?"

"Sophie," Langdon said quietly, "it's important to remember that the ancients' view of sex was entirely opposite from ours today. Sex begot new life -- the ultimate miracle -- and miracles could be performed only by a god. The ability of the woman to produce life from her womb made her sacred. A god. Intercourse was the revered union of the two halves of the human spirit -- male and female -- through which the male could find spiritual wholeness and communion with God. What you saw was not about sex, it was about spirituality. The Hieros Gamos ritual is not a perversion. It's a deeply sacrosanct ceremony."

His words seemed to strike a nerve. Sophie had been remarkably poised all evening, but now, for the first time, Langdon saw the aura of composure beginning to crack. Tears materialized in her eyes again, and she dabbed them away with her sleeve.

In the Temple, no less. Early Jews believed that the Holy of Holies in Solomon's Temple housed not only God but also His powerful female equal, Shekinah.

He gave her a moment. Admittedly, the concept of sex as a pathway to God was mind-boggling at first. Langdon's Jewish students always looked flabbergasted when he first told them that the early Jewish tradition involved ritualistic sex.

"For the early Church," Langdon explained in a soft voice, "mankind's use of sex to commune directly with God posed a serious threat to the Catholic power base. It left the Church out of the loop, undermining their self-proclaimed status as the sole conduit to God. For obvious reasons, they worked hard to demonize sex and recast it as a disgusting and sinful act. Other major religions did the same."

Men seeking spiritual wholeness came to the Temple to visit priestesses -- or hierodules -- with whom they made love and experienced the divine through physical union. The Jewish tetragrammaton YHWH -- the sacred name of God -- in fact derived from Jehovah, an androgynous physical union between the masculine Jah and the pre-Hebraic name for Eve, Havah.

Langdon decided not to shock his students with the fact that more than a dozen secret societies around the world -- many of them quite influential -- still practiced sex rites and kept the ancient traditions alive. Tom Cruise's character in the film Eyes Wide Shut discovered this the hard way when he sneaked into a private gathering of ultra elite Manhattanites only to find himself witnessing Hieros Gamos. Sadly, the filmmakers had gotten most of the specifics wrong, but the basic gist was there -- a secret society communing to celebrate the magic of sexual union.

Sophie was silent, but Langdon sensed she was starting to understand her grandfather better.

Ironically, Langdon had made this same point in a class lecture earlier this semester. "Is it surprising we feel conflicted about sex?" he asked his students. "Our ancient heritage and our very physiologies tell us sex is natural -- a cherished route to spiritual fulfillment -- and yet modern religion decries it as shameful, teaching us to fear our sexual desire as the hand of the devil."

Sophie's forehead felt cold as she pressed it against the plane's window and stared blankly into the void, trying to process what Langdon had just told her. She felt a new regret well within her. Ten years. She pictured the stacks of unopened letters her grandfather had sent her. I will tell Robert everything. Without turning from the window, Sophie began to speak. Quietly. Fearfully.

All the men in the audience leaned forward, listening intently.

"The next time you find yourself with a woman, look in your heart and see if you cannot approach sex as a mystical, spiritual act. Challenge yourself to find that spark of divinity that man can only achieve through union with the sacred feminine." The women smiled knowingly, nodding.

Langdon chuckled, not about to take the bait. From what he'd heard about Harvard parties, these kids were having more than enough sex. "Gentlemen," he said, knowing he was on tender ground,"might I offer a suggestion for all of you. Without being so bold as to condone premarital sex, and without being so naive as to think you're all chaste angels, I will give you this bit of advice about your sex lives."

"Professor Langdon?" A male student in back raised his hand, sounding hopeful. "Are you saying that instead of going to chapel, we should have more sex?"

The men exchanged dubious giggles and off-color jokes.

Langdon sighed. College men were still boys.

The women and men were staggered, black, white, black, white. The women's beautiful gossamer gowns billowed as they raised in their right hands golden orbs and called out in unison, "I was withyou in the beginning, in the dawn of all that is holy, I bore you from the womb before the start of day."

As she began to recount what had happened that night, she felt herself drifting back… alighting in the woods outside her grandfather's Normandy chateau… searching the deserted house in confusion… hearing the voices below her… and then finding the hidden door. She inched down the stone staircase, one step at a time, into that basement grotto. She could taste the earthy air. Cool and light. It was March. In the shadows of her hiding place on the staircase, she watched as the strangers swayed and chanted by flickering orange candles.

I'm dreaming, Sophie told herself. This is a dream. What else could this be?

The women lowered their orbs, and everyone rocked back and forth as if in a trance. They were revering something in the center of the circle.

What are they looking at?

The men responded, "She has her dwelling in eternity!"

"The woman whom you behold is love!" The women called, raising their orbs again.

In that instant, Sophie could finally see what they were all watching.

The chanting grew steady again. Accelerating. Thundering now. Faster. The participants stepped inward and knelt.

Sophie wanted to turn and run, but she couldn't. The stone walls of the grotto imprisoned her as the chanting rose to a fever pitch. The circle of participants seemed almost to be singing now, the noise rising in crescendo to a frenzy. With a sudden roar, the entire room seemed to erupt in climax.

The voices accelerated now. Louder. Faster.

Straddling her grandfather was a naked woman wearing a white mask, her luxuriant silver hair flowing out behind it. Her body was plump, far from perfect, and she was gyrating in rhythm to the chanting -- making love to Sophie's grandfather.

On a low, ornate altar in the center of the circle lay a man. He was naked, positioned on his back, and wearing a black mask. Sophie instantly recognized his body and the birthmark on his shoulder. She almost cried out. Grand-père! This image alone would have shocked Sophie beyond belief, and yet there was more.

Sophie could not breathe. She suddenly realized she was quietly sobbing. She turned and staggered silently up the stairs, out of the house, and drove trembling back to Paris.