“I remember that they’re the numbers that you can’t divide anything into,” Nina said. “Am I saying it right?”

“Sure. They’re the basic building blocks all the other numbers consist of. But they have a devilish aspect. They appear randomly on the positive number line. There’s no satisfactory algorithm that identifies them in sequence, and with large numbers it’s almost impossible to find the factors and determine if the numbers are prime or not.”

“So what?” Nina said.

“So what, you ask. Well, if we can’t find a formula to predict such a basic and crucial number sequence, we look like clowns, and the whole orderly system of mathematics we’ve built up over twenty-five hundred years looks like a pile of shit,” McGregor said. “It’s the black hole at the center of this area of human knowledge. We don’t even know what the fuck prime numbers are. Maybe they’re aliens from outer space sent to drive us crazy.”

“Oh. Aliens. Sure.”

“Riemann gave us a big clue about the behavior of the primes a hundred fifty years ago, but nobody has managed to take full advantage of it. Until his hypothesis is proved, we’re all a bunch of buffoons. Same with Cantor’s work on infinity. Until we figure out what to do with series that diverge, we may as well admit our whole mathematics system is a joke.”

“I see.”

“We’re screwed at the source. If my students had any idea how shaky math really is, they’d run screaming over to the English department.”

“That would be pretty dire,” Nina said. “May I ask, how are things with you?”

“My wife left me. I was thinking of coming to see you, then when you came here, I thought you must be representing her. I almost took off running, like I said. Reminds me of the old hermit mathematician who cracked open his door to some colleagues and said, ‘Please come at another time and to another person.’ ”

“Well, I’m not here to harass you.”

“And they’re not renewing my contract here. I had an affair with a student.” He had the grace to look embarrassed.

Nina gave him her card. “Any time,” she said. “But right now, I need help on this case.”

“Okay. Brown, Boston, Riemann.” He turned to his computer and clicked a few times with his mouse.

“ Brown University,” he said. “ Amherst. Northeastern. Brandeis. BU. MIT. The Big H. To name a few. Have some coffee and don’t interrupt me.” The thermos he pointed to was almost empty, but Nina took the last drop. McGregor clicked away, grunting occasionally to himself.

The campus was quiet. Occasionally a bird twittered, a squirrel chittered, or a student littered-no, muttered with another student, passing by. Not bad, acres of wooded park near a world-famous mountain lake, a state-of-the-art campus, friendly registrars-not her memory of college, but then, that was so long ago.

“Bingo,” Mick said dourly. “Got him. Come around the desk.” She jumped up and came around to where the sun made it hard to see the screen.

“Gottlieb Braun,” he said. “I’ve even heard of him. He hangs with the giants at MIT. Massachusetts Institute of Technology.” He sang to the tune of The Mickey Mouse Club song, “M-I-T, P-H-D, M-O-N-E-Y.”

He added, “That’s a song the envious folks at Caltech sing, by the way, not the one they sing at MIT. Well, okay, they sing it at MIT but the difference is, at MIT they think it’s funny.”

“How do you know it’s the right Brown?”

“Come over here.” She put her case on the ground and walked over to stand behind his chair. “Look,” he said.

Focusing on the MIT site, they reviewed the research interests of the math faculty. Dr. Braun was listed as being interested in “Areas Bridging Discrete and Continuous Math, Riemann Hypothesis, Continuum Hypothesis, Continued Fractions.”

“A number hound. A real throwback,” Mick said. “None of the other colleges I checked with had Browns with these kinds of research interests. Ready for a conjecture? Your student is one of his. Or was.”

“How sure are you?”

“What a question. I’m guessing, baby.” He raised and lowered his eyebrows at her, shot a look at her legs, then cleared his throat to distract her from his crassness.

She pressed on. “Gottlieb, huh?”

“A lot of the great mathematicians are from Central Europe. Lots of Germans. It all started with Gauss at Göttingen.”

“They’re fond of G’s, too, I guess.”

“Hmm, ‘Frequency of Letter G in Topics Related to the Math Profession.’ Don’t get me thinking thoughts like that. I need to sleep tonight.”

“Mick, I owe you.”

McGregor smiled at her and said, “Really?”

“You have my card. Thanks for this. And sorry to hear about your job. You’ll land somewhere better.”

“Give the Herr Professor my regards. A nondescript from the hinterland sends his respects.” He turned back to his computer, clicking furiously.

“See you, Mick.”

“High probability of that.”

Nina felt so excited she almost ran the red light at Al Tahoe and Lake Tahoe Boulevard. Back at the office, Sandy had laid her brown-bag lunch out on the desk. “Looks yummy,” Nina said. Tossing her jacket on the chair, she revved up her Mac and went straight to MIT, or the simulacrum thereof on the Web.

Sandy came in and deposited a sandwich wrapped in waxed paper and a can of cola on her desk. “Mangia,” she said.

“I’ve got the Brown,” Nina said. “Maybe.”

“If you don’t eat lunch you’ll starve, drop to the floor, and never find out anything else.”

Nina tore open the sandwich. Liverwurst and mayonnaise. Worse things had been turned into sandwiches, although she couldn’t think what they were offhand. She ate, clicking and navigating with her free hand. Sandy sat down with a legal pad. “Well?”

“Braun’s in Room 2-181 at MIT. Write down this phone number and E-mail. Here’s a photo of him. Pale blue suit jacket, red tie, black hair, specs. It’s his birthday. His sixteenth, to go by his looks. He’s very young for a professor, isn’t he? Mud-colored birthday cake, most pathetic-looking cake I have ever seen. Take a look at those sprinkles, the festive arrangement of yellows on brown.”

“You’re forgetting the one you made for Bob’s twelfth birthday. Remember?”

Nina remembered. “The great thing was, he thought I did it intentionally.”

“It took guts, serving that thing to friends.”

“Yeah, I’ve got guts all right. Guts enough to put up with you and him both. Okay, back to our picture. There are students in the photo. No boys from India, no girls. Dreadful lighting that washes the blood out of everybody.”

“Keep going.”

“Braun was a finalist for the Abel Prize. I think that’s like the Nobel, only it’s given for math. He’s a big shot, a full professor, even though he’s young. Okay, the math department: fifty-two faculty members, thirty instructors, one hundred twenty-five grad students, and they graduate about one hundred forty undergraduates a year.”

“Let’s check more photos.” Sandy edged around so that she could look with Nina. Additional pictures of student-faculty gatherings documented an unfortunate reliance on those rectangular brown cakes, which must have been a local caterer’s specialty. A couple of girls here and there joined the company, but didn’t seem to match the description of their witness.

The boys caught milling around in the photos looked conventional, except that a few were shaky on style, wearing short-sleeved oxford and plaid flannel shirts, the kind of thing that might have been sold at the Harvard Coop circa 1951. Hair ran the gamut from slickly modern to huge frizz to fifties executive. Chalked-up blackboards tended to dominate the backgrounds.

“They’re so pale, like slugs slithering out from under a rock,” Sandy said, disapproving. “I bet they never go outside.”

“They eat cake and trade fashion tips instead. But let’s not be unkind,” Nina said. “So what if they don’t sweat the small stuff?”