I will go mad, he sometimes thought. It seemed something he could choose, as if he were a character in an Elizabethan drama who turns to the audience to announce that he will be mad now, and then in the next scene is found gnawing bones dug out of the family sepulcher. Davout could see himself being found outside, running on all fours and barking at the stars.

And then, as dawn crept across the windowsill, he would look out the window and realize, to his sorrow, that he was not yet mad, that he was condemned to another day of sanity, of pain, and of grief.

Then, one night, he did go mad. He found himself squatting on the floor in his nightshirt, the room a ruin around him: mirrors smashed, furniture broken. Blood was running down his forearms.

The door leapt off its hinges with a heave of Old Davout’s shoulder. Davout realized, in a vague way, that his sib had been trying to get in for some time. He saw Red Katrin’s silhouette in the door, an aureate halo around her auburn hair in the instant before Old Davout snapped on the light.

Afterward Katrin pulled the bits of broken mirror out of Davout’s hands, washed and disinfected them, while his sib tried to reconstruct the green room and its antique furniture.

Davout watched his spatters of blood stain the water, threads of scarlet whirling in coreolis spirals. "I’m sorry," he said. "I think I may be losing my mind."

"I doubt that." Frowning at a bit of glass in her tweezers.

"I want to know."

Something in his voice made her look up. "Yes?"

He could see his staring reflection in her green eyes. "Read my downloads. Please. I want to know if… I’m reacting normally in all this. If I’m lucid or just…" He fell silent. Do it, he thought. Just do this one thing.

"I don’t upload other people. Davout can do that. Old Davout, I mean."

No, Davout thought. His sib would understand all too well what he was up to.

"But he’s me!" he said. "He’d think I’m normal!"

"Silent Davout, then. Crazy people are his specialty."

Davout wanted to make a mudra of scorn, but Red Katrin held his hands captive. Instead he gave a laugh. "He’d want me to take Lethe. Any advice he gave would be… in that direction." He made a fist of one hand, saw drops of blood well up through the cuts. "I need to know if I can stand this," he said. "If-something drastic is required."

She nodded, looked again at the sharp little spear of glass, put it deliberately on the edge of the porcelain. Her eyes narrowed in thought-Davout felt his heart vault at that look, at the familiar lines forming at the corner of Red Katrin’s right eye, each one known and adored.

Please do it, he thought desperately.

"If it’s that important to you," she said, "I will."

"Thank you," he said.

He bent his head over her and the basin, raised her hand, and pressed his lips to the flesh beaded with water and streaked with blood.

It was almost like conducting an affair, all clandestine meetings and whispered arrangements. Red Katrin did not want Old Davout to know she was uploading his sib’s memories-"I would just as soon not deal with his disapproval"-and so she and Davout had to wait until he was gone for a few hours, a trip to record a lecture for Cavor’s series on Ideas and Manners.

She settled onto the settee in the front room and covered herself with her fringed shawl. Closed her eyes. Let Davout’s memories roll through her.

He sat in a chair nearby, his mouth dry. Though nearly thirty years had passed since Dark Katrin’s death, he had experienced only a few weeks of that time; and Red Katrin was floating through these memories at speed, tasting here and there, skipping redundancies or moments that seemed inconsequential…

He tried to guess from her face where in his life she dwelt. The expression of shock and horror near the start was clear enough, the shuttle bursting into flames. After the shock faded, he recognized the discomfort that came with experiencing a strange mind, and flickering across her face came expressions of grief, anger, and here and there amusement; but gradually there was only a growing sadness, and lashes wet with tears. He crossed the room to kneel by her chair and take her hand. Her fingers pressed his in response… she took a breath, rolled her head away… he wanted to weep not for his grief, but for hers.

The eyes fluttered open. She shook her head. "I had to stop," she said. "I couldn’t take it-" She looked at him, a kind of awe in her wide green eyes. "My God, the sadness! And the need. I had no idea. I’ve never felt such need. I wonder what it is to be needed that way."

He kissed her hand, her damp cheek. Her arms went around him. He felt a leap of joy, of clarity. The need was hers, now.

Davout carried her to the bed she shared with his sib, and together they worshipped memories of his Katrin.

"I will take you there," Davout said. His finger reached into the night sky, counted stars, one, two, three… "The planet’s called Atugan. It’s boiling hot, nothing but rock and desert, sulphur and slag. But we can make it home for ourselves and our children-all the species of children we desire, fish and fowl." A bubble of happiness filled his heart. "Dinosaurs, if you like," he said. "Would you like to be parent to a dinosaur?"

He felt Katrin leave the shelter of his arm, step toward the moonlit bay. Waves rumbled under the old wooden pier. "I’m not trained for terraforming," she said. "I’d be useless on such a trip."

"I’m decades behind in my own field," Davout said. "You could learn while I caught up. You’ll have Dark Katrin’s downloads to help. It’s all possible."

She turned toward him. The lights of the house glowed yellow off her pale face, off her swift fingers as she signed.

Regret "I have lived with Old Davout for near two centuries," she said.

His life, for a moment, seemed to skip off its internal track; he felt himself suspended, poised at the top of an arc just before the fall.

Her eyes brooded up at the house, where Old Davout paced and sipped coffee and pondered his life of Maxwell. The mudras at her fingertips were unreadable in the dark.

"I will do as I did before," she said. "I cannot go with you, but my other self will."

Davout felt his life resume. "Yes," he said, because he was in shadow and could not sign. "By all means." He stepped nearer to her. "I would rather it be you," he whispered.

He saw wry amusement touch the corners of her mouth. "It will be me," she said. She stood on tiptoe, kissed his cheek. "But now I am your sister again, yes?" Her eyes looked level into his. "Be patient. I will arrange it."

"I will in all things obey you, madam," he said, and felt wild hope singing in his heart.

Davout was present at her awakening, and her hand was in his as she opened her violet eyes, the eyes of his Dark Katrin. She looked at him in perfect comprehension, lifted a hand to her black hair; and then the eyes turned to the pair standing behind him, to Old Davout and Red Katrin.

"Young man," Davout said, putting his hand on Davout’s shoulder, "allow me to present you to my wife." And then (wisest of the sibs), he bent over and whispered, a bit pointedly, into Davout’s ear, "I trust you will do the same for me, one day."

Davout concluded, through his surprise, that the secret of a marriage that lasts two hundred years is knowing when to turn a blind eye.

"I confess I am somewhat envious," Red Katrin said as she and Old Davout took their leave. "I envy my twin her new life."

"It’s your life as well," he said. "She is you." But she looked at him soberly, and her fingers formed a mudra he could not read.

He took her on honeymoon to the Rockies, used some of his seventy-eight years’ back pay to rent a sprawling cabin in a high valley above the headwaters of the Rio Grande, where the wind rolled grandly through the pines, hawks spun lazy high circles on the afternoon thermals, and the brilliant clear light blazed on white starflowers and Indian paintbrush. They went on long walks in the high hills, cooked simply in the cramped kitchen, slept beneath scratchy trade blankets, made love on crisp cotton sheets.