“No. You go down first.”

“Matthew, I’m an electronically generated image. What difference does it make whether I’m up here or down there?”

“I’m not sure. But it’s like you’re a component of the ship. When you’re outside, you have less power.”

“That’s very scientific.”

“Like a machine that only works if one person pushes the button.” He kept the pistol where it was and made a sideways gesture with his head.

La shrugged and walked down the ramp.

Matt worried the time machine out of its bracket and freed the alligator clip. “Are you okay?”

“I’ve been better.” Martha touched her breasts gently. “That was . . . you weren’t going to . . .”

“I wouldn’t, no. Let’s go down and see what happens.” Matt kept the pistol trained on the machine as they walked down the ramp. The air was cold but still, and smelled clean.

La was standing there with her arms crossed, not quite tapping a toe. “So how long will it be before Jesus comes to save you?”

“He wasn’t Jesus last time,” Matt said. “More like Saint George, looking for a dragon.”

“Well, if it’s me, here I am.” She looked over their heads. “And here he is. If I’m not mistaken.”

A shimmering globe half the size of the ship was descending. When it touched the ground, it disappeared like a soap bubble. Six men, or manlike creatures, stood where it had been.

Four of them seemed to be human. The one with the pear-shaped head had scales for skin. The other’s features were not fixed; it had two or more eyes and a recognizable mouth, but they constantly disappeared and reappeared elsewhere.

“Hello, Matthew. Martha.” Their savior still had a Jesus beard, but, like the others, was draped in what looked like mail. “Martha, if you would, please go back into the ship and get a day’s worth of food and water for you both. And anything else you want to take back.” She hurried back up the ramp.

“La. So you want to go all the way up.”

“That’s right. The heat death of the universe.”

“I can do that for you.” He held out his hand. “The machine, Matthew?”

He hesitated. “We won’t need it anymore?”

“Not unless you want to go with La. Believe me, the future doesn’t get any better on Earth. I’ve been there. It’s a closed book.”

Matt couldn’t figure out any way that the man might be betraying them. They were at his mercy anyhow. He handed it over.

“Thank you. You may call me, um, Jesse.” He sat down cross-legged, the machine in his lap. “You couldn’t pronounce my real name.”

His right forefinger became a motorized screwdriver. He undid the eight screws that held the cover on and set it carefully aside, slowly studying the wires that connected the top to the insides.

He gently tugged on a gray box inside the box, and it popped free.

“The virtual graviton generator?” Matt said.

“What else?” He pulled an identical-looking box from a pocket in his tunic. He pressed it home with a sharp click. “Voil а !”

“So what does that do?” La asked.

“Yeah,” Matt said.

Jesse looked at his companions and said something in a language that was mostly whistling. The human ones laughed. The pear creature made a noise like crab claws scuttling on wood. The other one’s mouth disappeared and reappeared.

“Neither of you would understand. You don’t have the math—you don’t have the worldview to understand the math.” He positioned the top cautiously and screwed it down tight. Martha came back with the bag, which was considerably heavier.

Jesse stood with balletic grace and handed the box to La. “Now the button works no matter who touches it.”

“I have only your word for that. How do I know it won’t explode?”

“You don’t,” he said cheerfully. “But you are the only entity here who’s not alive—not in any biological sense— and you’re worried about dying?”

“Dying is not the opposite of existing.”

“I guess you’ll just have to trust me. As these two must.”

She took the box and looked at Matt. “It’s been interesting. ” She walked up the ramp with it, and less than a minute later, the ship disappeared with a faint pop.

“She’s on her way?” Matt said.

Jesse nodded, looking at the space where the ship had been. “I’ve never tried to go so far up. I assume the thing will keep working, but asymptotically.”

“She’ll get closer and closer, but never quite be there?”

“As she must have known. As long as she can still push the button, the show isn’t over. By definition.”

“Why did you help her?” Martha said. “And why are you helping us?”

“With her, it’s just courtesy. People, or nonpeople, get stuck in time. Other time travelers unstick them.

“With you, it’s not so altruistic. If you, Matthew, were to die before going back, this whole bundle of universes would disappear.”

“If I hadn’t discovered the time machine?”

“Well, you didn’t actually ‘discover’ anything, did you? You just used a component that was faulty in a dimension you can’t even sense. Like the family dog accidentally starting the car. Not to be impolite.

“We’ve sent you back before.” He rubbed his brow. “Words like ‘before’ and ‘after’ become inadequate. But we have sent you back to 2058 to bail yourself out, a large number of times. We know that because we’re still here. All of us are your descendants, in a way. If time travel hadn’t started in your time and place, we wouldn’t exist.”

“Even the, um . . .” He made a helpless gesture. “The aliens?”

Jesse said something in the whistling language. The one with the scales made his crab-claw noise and the other one’s face filled up with eyes. “They’re at least as human as you are.” Martha smiled at that.

“Sorry. Sorry.” The two strange ones bowed. “So do you have a time machine?”

“The six of us area time machine.” He pulled out the virtual graviton generator. “You have to both be touching this, for calibration. It will send you back to where Matt first pushed the button.

“But there’s something like an uncertainty principle involved. We can send you back to the exact time or the exact place, but not both.”

“Time, then,” Matt said. “We can find our way back to Cambridge.”

“Well, no. Not if you appear a mile under the sea, or inside a mountain. I’d choose place, if I were you.

“You might be only a few seconds off, or you might be years. We have no control over that. Was your lab on the ground floor?”

“It was, yes.”

“If it weren’t, you’d appear on the bottom floor beneath it. If you’re in a future or a past where the lab doesn’t exist, you’ll appear at ground level where it was or will be.”

“What if I meet myself and say, ‘Don’t push that button’? ”

“It won’t happen. You can’t exist, as your former self, in this universe. When we’ve sent you back to 2058, your copy automatically showed up in a time when you were in transit, and left before you reappeared.”

Matthew rubbed his chin. “I can do anything I want? I could reinvent the time machine?”

Jesse paused. “We know that you haven’t. You could try; the dog could start the car again. But it wouldn’t be smart; you’d be well advised not to put yourself in the public eye. You’d look very suspicious if someone investigated your past. If you claimed to be a time traveler, you’d probably be locked up.”

“Even if we appear in the future?”

“Even so. You won’t have existed; there would be no Marsh Effect.”

“At least the bastard won’t win a Nobel Prize.”

“You never know.” He handed the gray box to Matt. “Are you ready?”

Matt looked at Martha. She managed a weak smile and nodded. She touched the box and he folded his other hand over hers. She did the same.

“Good luck,” Jesse said. The others murmured, whistled, and scraped similar sentiments.

There was no interlude of gray. One moment they were in the Antarctic waste, and the next, they were ankle deep in mud. It was a cool fall day. A few hundred yards away, workmen were toiling at the edge of the Charles River, building a seawall.