“Sure. How’s he doing?”

“All right. Assistant professorship, tenure. Has a family, I believe.”

“Oh. How nice.”

Marsh paused. He was not completely clueless. “You outrank him, of course. Honorary full professor, and tenure is, um . . .” He waved it away with one hand. “You’re the safest person in the department. After me, perhaps.”

“So I’ll be teaching . . . not chronophysics.”

“No, no, not yet. You have some catching up to do. We have you penciled in for 8.225.”

“Doesn’t ring a bell.”

“It’s an introduction to old modern physics—‘Physics of the Twentieth Century’—you know, Einstein, Oppenheimer, Feynman.”

“Twentieth century?” Marsh nodded. “Jesus!”

“A lot has happened in physics since you disappeared,” he said. “ Becauseyou disappeared. There are even aspects of Newtonian mechanics that have to be reconsidered. String theory’s completely rewritten, and with it, quantum mechanics and relativity—moving toward a Grand Unified Theory, finally.

“These past fifteen years have seen a total revolution. People compare it to the 1920s, after Einstein’s bombshell.”

“So I have some studying to do.”

“Quite a lot, I think.” He reached into his bag and brought out two books, one at a time: Aspects of Time Traveland Intermediate Chronophysics, both by himself. “You might want to look through this one first.” Aspects.“You’ll want to bone up on rings and algebras and topology for Intermediate.”

Rings and algebras? “What does set theory have to do with it? Topology?”

“I think you’ll find it an interesting approach. But do read the general treatment first.” He levered himself up out of the chair, wincing. “If you feel up to contributing, we’ll be having a press conference at noon. The big conference room on the fourth floor of the Green Building.”

“No harm in it. Not much to tell them.”

“See you there about 11:30, then. Think I’ll go have a little rest first.” He shook hands and shuffled away.

Matt was halfway through the book’s introduction when there was a tap on the door. “Mattie?” It was Kara, a little heavier, poised on the brink of middle age, still attractive in a short skirt and SPAMIT tee shirt—Stupid People at MIT, a select fraternity. Strom Lewis followed her in, not quite a young Turk anymore, salt-and-pepper in a short beard.

She giggled, hand in front of her mouth, then shrugged off her backpack and kissed him on the cheek. “You look so young!”

He couldn’t immediately come up with a tactful reply— “You look so old” wouldn’t be kind—so he just nodded.

“By God,” Strom said. “Was it like . . . I mean, did no time pass at all?”

“Less than a minute each time, each transition,” Matt said. “I was in Somerville yesterday, at the police department’s stolen automobile pound.”

“I’d forgotten about that,” Strom said. “That must have been pretty unpleasant.”

Did people know about the mysterious stranger with the million bucks’ bail? It had to be a matter of record. “What about when I came back for a few seconds on the express-way? Fifteen years ago. Was anybody hurt?”

They looked at each other. “There was a big pileup,” Kara said. “I don’t remember whether anyone was hurt or killed.”

“Well, yeah,” Strom said. “I’ve seen the cubes a hundred times. A pickup truck rolled, but I think the driver stayed inside—that’s right; you can see an air bag. Other cars banging around. One was a police ghost car, fortunately, so we had your appearance time down to the thousandth of a second, and with five or six different GPS readings, we could position you within a fraction of a millimeter.”

“So if I pushed the button now? Would I wind up in Arizona, or what?”

“Up by the New Hampshire border, I think, 177 years from now. Of course, no one’s going to push the button until we have a duplicate made.”

“Okay by me. Fifteen years is disorienting enough.”

“Oh, I brought you some stuff,” Kara said, and rummaged through her backpack. She brought out a stack of magazines and a thing like an old-fashioned iPod stick, but without wires. “Here.” She pulled a little red dot off the machine and pressed it onto his cheekbone. “I put some old music on it, too, but it’s mainly what young people are listening to. Your students’ ages.”

“Pure crap,” Strom said.

“No, it’s just different.” She did a shrug and a moue that hadn’t changed. “They look different, too.”

“Brands,” Matt said. “I’ve seen a few here.”

“And other kinds of scars. Not so much at MIT. It can be pretty extreme on the street.” She put the magazines on the rolling table by the bed. “You’ll want to look through these.”

Strom stood up. “Once you get settled, come on up to the office. Spend a few hours getting you up to speed on the math.”

“Yeah . . . I’ll Google around for a few days first, get my bearings.” Have to ask. “Um . . . does anybody know who bailed me out?”

“Bailed you out?”

“The first time I came back, after forty days?”

“Of course,” Strom said. “That’s when you sent the preliminary results to Dr. Marsh.”

“That’s right. I was in jail for causing a pileup on Mass Ave. A lawyer showed up with my bail, which he got from some anonymous stranger.”

Strom shook his head. “I don’t know anything about that. Could it have been Marsh?”

“No way. He was . . . sort of angry with me.”

“I remember,” Kara said. “He got my number somehow and called me. He thought you’d stolen the machine and disappeared. Of course you’d just—”

“But I left him a duplicate! Slogged down here in the snow to put it together. It didn’t travel through time, but it did supply one photon per chronon, which is what it was designed to do.”

“He must not have found it.”

“But I put it right where . . . I’ll take it up with him later today.” Could somebody have broken in and stolen it? Nobody would know of its importance.

Except perhaps a time traveler.

“Well, we’ll see you over at the press conference,” Strom said. “Come early. I heard Marsh talk to Maggie about the catering. It’s going to be a real blowout.”

“Sounds good. I’ll see about checking out of here.” He watched them go with mixed, not to say confused, feelings. Just a few days ago, they had destroyed his life. Now they were strangers and allies.

The suitcase in the closet was his, but most of the clothes hanging there were unfamiliar. Once they’d realized what had happened, the department had rented his old place, partly to keep it against his return and partly to see if there was any clue there to the machine’s anomalous behavior.

Most of the clothes he’d left behind had been ten years old already, and not too clean. Another fifteen years wouldn’t have helped.

It looked pretty warm out. He put on an unfamiliar tie and tweed jacket. Stroll through campus and check out the current crop of undergraduate girls. Brands and all.

The dispatcher at the main desk said that everything had been taken care of; he was free to go. An hour and a half before the press conference. Walk up to the Student Center and back, and get there just as the canapйs come out.

He was headed for the revolving door when the emergency doors next to it whooshed open. Two men and a woman rushed in guiding a gurney.

It was Professor Marsh, mouth open and eyes closed. They pushed him into a waiting elevator.

Matt went back to the dispatcher. “Is that Professor Marsh?”

“Was, I think.” He squinted at his computer screen. “Somebody found him in the Green Building, in his office. We had this team there for a big press conference; they got right to him. Too late, though.”

“Damn.”

“I saw him on TV last night,” the dispatcher said. “Too much excitement, I guess. You knew him?”

“A long time ago, yeah.”

“How old was he?”

“Sev—eighty-five or so. Closer to ninety.”