Pierre tried to ignore the way Avi Meyer was looking at him. It had been twenty-six months since they’d last seen each other face-to-face, and although Pierre had told Avi over the phone about his condition, Avi had not until today actually seen Pierre’s chorea.

Pierre slowly, carefully, laid two autoradiographs on the light table set into his lab’s countertop, and then, with dancing hands, tried to line them up side by side. He seated himself on a lab stool, then motioned for Avi to come over and look at the autorads. “All right,” said Pierre, “what do you see?”

Avi shrugged, not knowing what Pierre wanted him to say. “A bunch of black lines?”

“Right — almost like blurry versions of the bar codes you see on food boxes. But these bar codes” — he tapped one of the pieces of film with a trembling finger — “are DNA fingerprints of two different people.”

“Who?”

“I’ll get to that in a minute. You see that the bar codes are quite different, right?”

Avi nodded his bulldog head.

“There’s a thick black line here,” said Pierre, pointing with a trembling finger again, “and there’s no corresponding black line at the same point on the other one, right?”

Avi nodded again.

“But some of the lines are the same, aren’t they? Here’s a thin line, and — look! — the other person has a thin line at exactly the same point.”

Avi sounded impatient. “So he does.”

“Now, have a good close look at the two fingerprints, and tell me by how much you think they overlap.”

“I don’t see what this—”

“Just do it, will you?”

Avi sighed in resignation and squinted his tiny eyes at the film. “I don’t know. Twenty or thirty percent.”

“About a quarter, in other words.”

“I guess.”

“A quarter. Now, you must know something about genetics — everybody does. How much DNA do you get from your parents?”

“All of it.”

Pierre grinned. “That’s not what I meant. I mean, what proportion comes from your mother and what proportion from your father?”

“Oh — it’s half and half, isn’t it?”

“Exactly. Of all the DNA that makes up a human being, precisely half comes from each parent. Now, tell me this: do you have a brother?”

“Yes,” said Avi.

“Okay, good. Now if you’ve got half of your mother’s DNA, so does your brother, right?”

“Sure.”

“But is it the same half?”

Avi ran a hand over the stubble on his face. “How do you mean?”

“Is the DNA you got from your mother the same or different from what your brother got?”

“Well, I don’t know. I guess if I got a random selection of my mother’s genes, and Barry got a random selection, they’d overlap by — what? — fifty percent?”

“That’s right,” said Pierre, not nodding deliberately, but his head bobbing in a way that looked as though he was. “An average of fifty percent overlap. So, if I put DNA fingerprints for you and your brother side by side, what would you expect to see?”

“Umm — half of my bars at the same places as half of his bars?”

“Exactly! But what have we here?” He pointed to the two pieces of film on the illuminated panel.

“A twenty-five percent overlap.”

“So these two people are highly unlikely to be brothers, right?”

Avi nodded.

“But, still, they do seem to be related, don’t they?”

“I guess,” said Avi.

“Okay. Now there’s something I read when I first looked into this case that has stuck in my mind. On his application for refugee status, John Demjanjuk put his mother’s maiden name as Marchenko.”

“Yeah, but that was wrong. Her maiden name was Tabachuk.

Demjanjuk couldn’t remember it, he said, so he just put down a common Ukrainian name.”

“And that always struck me as strange. I know my mother’s maiden name, Menard — and her mother’s maiden name, Bergeron. How could someone not remember his own mother’s maiden name? After all, Demjanjuk filled out that form in the 1940s, while he was still in his twenties. It’s not like he was an old man with a failing memory.”

Avi shrugged. “Who knows? The point is he couldn’t remember it at the time.”

“Oh, I think he remembered very well — but rather that he didn’t understand the question.”

“What?”

“He didn’t understand the question. Tell me — what does the term ‘maiden name’ mean?”

Avi frowned, irritated. “The name a woman was born with.”

“Right. But suppose Demjanjuk — who, according to the articles I read, only had a fourth-grade education — suppose he thought it meant simply the name his mother had before she’d married his father.”

“That’s the same thing.”

“Not necessarily. It’s only the same thing if his mother had never been married before.”

“But — oh, shit. Shit, shit, shit.”

“You see? What was Demjanjuk’s mother’s first name?”

“Olga. She died in 1970.”

“If Olga had been born Olga Tabachuk, but had married a man named Marchenko and then later divorced him before marrying John Demjanjuk’s father—”

“—Nikolai Demjanjuk—”

“—then when asked his mother’s maiden name, and interpreting it as meaning his mother’s previous name, John Demjanjuk would have answered ‘Marchenko.’ And if Olga had had one son named Ivan in 1911 by this elder Marchenko, and another son named Ivan nine years later by Nikolai Demjanjuk, then—”

“Then Ivan Marchenko and Ivan Demjanjuk would be half brothers!” said Avi.

“Exactly! Half brothers, having about twenty-five percent of their DNA in common. In fact, it even makes sense that they’re both bald. The gene for male-pattern baldness is inherited from the mother; it resides on the X chromosome. And it explains why they look so much alike — why witness after witness mistook one for the other.”

“But wait — wait. That doesn’t work. Nikolai and Olga Tabachuk were married January twenty-fourth, 1910, and Ivan Marchenko was born after that — on March second, 1911. That means he would have been conceived in the summer of 1910 — after Olga had already ended up with the legal last name of Demjanjuk.”

Pierre frowned for a moment, but then, thinking briefly of his own mother and Henry Spade, he exclaimed, “A triangle!”

Avi looked at him. “What?”

“A triangle — don’t you see? Think about John Demjanjuk’s own marriage from 1947. I remember reading that he’d been fooling around with another man’s wife while that man was away.” Pierre paused. “You know, we sometimes sum up the geneticist’s creed as ‘like father, like son’ — but ‘like mother, like son’ is just as valid for many things. My wife the behaviorist doesn’t like to admit it, but particular kinds of infidelity do run in families. Let’s say Olga Tabachuk married the senior Marchenko, divorced him, and then married Nikolai Demjanjuk.”

Avi nodded. “Okay.”

“But Nikolai leaves their village and heads out to — what town was Demjanjuk born in?”

“Dub Macharenzi.”

“To Dub-whatever. He goes there, looking for work or something like that, saying he’ll send for his wife once he’s got a place. Well, while the cat’s away… Olga goes back to sleeping with her ex, Marchenko. She gets pregnant and gives birth to Marchenko’s child, a child they name Ivan.

But then Nikolai sends word for her to come join him in Dub-thingie. Olga abandons baby Ivan, leaving him with the elder Marchenko. In fact — well, here’s one my wife would like: Ivan Marchenko grew up to have a predilection for slicing off women’s nipples. Call that his revenge for having been abandoned by his mother.”

Avi was nodding slowly. “You know, it makes sense. If Olga really did abandon the baby Ivan Marchenko, and if her second husband, Nikolai Demjanjuk, never knew about that incident, when she finally had a son of her own by Nikolai, that could explain why she decided to name him Ivan, too — so that she could never give herself away by accidentally referring to her legitimate son by the bastard child’s name.” Avi looked down at the autorads. “So — so one of these was made from the tissue specimen I sent you that we’d taken from John Demjanjuk, right?”