Not surprisingly, they dreamed of being able to spend an entire night together in safety and privacy. The sister raised the subject often, telling him just what she would like to do to him, and what she would have him do to her.

“ Maybe when we’re older,” she said. “When we’re both out of the house. Unless you find somebody else by then.”

But there would never be anybody else, he assured her. She was the only one he wanted.

What she didn’t point out in response, and what he knew without being told, was that what he wanted, what they both wanted, could never be. They were brother and sister. They could never be man and wife.

He couldn’t imagine himself with anyone else, couldn’t bear the thought of her in someone else’s arms. She was his and he was hers. How could he marry another woman, a stranger?

“ I thought of becoming a priest,” he told me. “If I couldn’t have her, then it would be easier if I never had to have anyone. Then the absurdity of the notion struck me. I was in bed with my sister, I was committing all kinds of sins with her, and the fact that I wouldn’t be able to go on committing them forever made me think I had a vocation. But I swear it seemed perfectly logical to me at the time.”

One day she had an idea. He was still a member of a Boy Scout troop, although he’d become less active. The troop had a camping weekend scheduled. Suppose he signed up for it? And suppose she drove to the encampment and picked him up down the road around the time the troop’s bugler blew Taps and turned in for the night? They could go to a motel-she’d take care of booking a room-and they could have a whole night together and get him back to camp before Reveille.

That’s what they did. On Friday night, he waited until his tent mate was sleeping, then slipped out and trotted down the road to where she was waiting. It was all set for the following night, she told him. The room was booked, and she’d bought some massage oil and something provocative to wear. She wished they could go there now, but she had to get home. She had an excuse lined up for her absence the following night, but not tonight, and she had to get home.