“Mine. He didn’t want to have the first thing to do with finding her. All he wanted to do was die.” He cocks his head to one side. “I guess you could say I accommodated him.” He tries to laugh again, only to produce a croak reminiscent of someone choking. “But like I said, I couldn’t let him stop me.”

Something in the ephemera on the walls steals Jonas’s attention. It’s faint, like a road sign on the horizon, but it’s there. Buried in the jumble of letters and symbols and numbers.

He rises and wanders to the east wall. He hadn’t had the chance to finish reviewing his counterpart’s work before. Slowly, the equations begin to take on meaning and substance, revealing a structure Jonas’s mind can grasp. He follows the equations down, lowering himself to the floor. On the baseboard is a calculation he’s never seen before. He works to make sense of the formulae, feeling Other Jonas watching him, slowly nodding encouragement. Go on. You can do it . . .

Jonas puts a hand to the baseboard. His fingers graze the equations there. He feels the same sensation he did two years ago, back in Stockholm, when he held a little piece of blue plastic marked by two blue lines that told him he was going to be a father.

He’s staring at a miracle.

“Thibault was wrong,” he exhales. Astonishment and relief. “He was wrong. There’s a second universe. Another universe where she’s still alive.” The words, the sound of hope, echo in his mind. She’s still alive. Jonas turns back to the equations. “And you found it.”

“Yes. And before you ask, that’s the last one.”

“Why didn’t you go there?” Jonas asks.

Other Jonas shrugs. “I’m trapped here.” He strains against the bedsheets holding him in place. “Even before you tied me to a chair.”

“I don’t understand.”

Other Jonas lets an exasperated sigh escape him. Then, as though to an obstinate student: “CERN’s Large Hadron Collider unanchored you, right? Like cutting away ballast, it allowed you to slip realities.” Jonas nods. “I did the same. The problem is, the effect wears off eventually. The quantum energies dissipate over time.”

Jonas had forgotten. He struggles for breath. The world becomes liquid.

“That’s what happened to me,” Other Jonas says. “I found out where Amanda is, where I needed to go, but not before I lost the ability to go there.” However long he’s been marooned in this reality hasn’t been long enough to erase the bitterness of this development.

“You have to be feeling it by now,” Other Jonas continues. “The sensation. The pain in your body. Each time you jump universes. You feel that tingling, don’t you?”

Jonas does. He had convinced himself that the pain was the result of all the abuse he had taken recently, a residual effect of his reality-slips, but he can’t deny that his body’s protestations emanate from a deeper place, in his very marrow. An unusual, inexplicable pain. The kind of pain reserved for disease instead of injury.

Other Jonas regards him. “You’ve been feeling the loss of the quantum effect.”

“What happens when it’s gone?” The words come out clipped.

“You’ll be trapped. Same as me.”

“How much time do I have?” Jonas asks, feeling like a condemned prisoner.

“Untie me, and we can find out.” Jonas returns a skeptical stare. “You know I can’t do that kind of math in my head. We can’t,” Other Jonas corrects. “I promise I won’t try to kill you.”

Jonas considers this and concludes that he has no choice but to take the risk. As he unties Other Jonas, he admonishes, “Try anything, and I’ll lay you out again. Apparently, in my reality, I work out more.”

“Cute,” Other Jonas says as he stands. “First, I’m going to need to examine your anchor.”

“What?”

Other Jonas points to Jonas’s tether. “That. Your anchor.”

“I call it a tether.’”

“Potay-to, potah-to.” Other Jonas shrugs as he moves toward the closet. The stench is much worse with the floorboards displaced, but it doesn’t seem to bother Other Jonas. He emerges with a thick object the size of a serving platter. An assembly of naked circuit boards, transistors, and microchips cluster atop it. Other Jonas rests it on the soiled bed and snakes out a fluorescent-orange power cord from the device, which he plugs into a nearby socket. “I need to see your anchor—your tether,” he corrects.

“I can’t take it off for long.”

“Tell me something I don’t know. But maybe you could be a touch more patronizing while you’re at it.” He points to a space in the center of the device, roughly the size of a hand. “Just rest your whole hand here.”

Jonas leans down to do as instructed, watching Other Jonas manipulate a series of microswitches affixed to the neat row of circuit boards. Jonas feels a slight tingle as electricity courses through him.

“How long will this take?” Jonas asks.

“As long as it takes.”

A small LCD screen comes to life in the corner of the rectangular device. A series of decimal numbers, like IP addresses, flash across the display. Jonas watches his doppelgänger study them.

“Give me a second,” Other Jonas says as he moves to the nightstand. “You can take your hand back.” He rifles through the papers piled atop the nightstand, turning over sheet after sheet until he spots one that’s clear of writing. From the drawer, he produces a pen and sets to work running the numbers he memorized from the LCD’s readout through a gauntlet of equations.

“Although your tether is designed to regulate the quantum radiation in your body, it also absorbed it at the same level and is leaking it in similar fashion. Which means the rate of energy dissipation can be measured.”

“You can figure out how many more times I can reality-slip,” Jonas says.

“Yes, but that’s only part of the problem.”

“What’s the other part?”

“I thought I was smarter than this,” Other Jonas sighs. “It’s very disappointing, I don’t mind telling you.”

“Don’t play games with me,” Jonas snaps.

“Actually, I’m playing games with me.”

Other Jonas taps his calculations with his pen. “If my math is right—which it is—you can untether yourself only two more times before you’re permanently stranded in whatever universe you end up in.”

“Only two more times,” Jonas breathes.

“And then you lose the ability to slip realities. Permanently.”

“Why? Why only two times?” Jonas demands.

“I told you: Your tether is leaking quantum radiation. It’s like a battery.” Other Jonas shrugs. “Batteries wear out.”

Jonas forces himself to accept the reality of this. “You said that was only part of the problem . . .”

“Yes. Before you lose the ability to reality-slip, you have to make sure that whichever reality you end up in has a particle collider.”

“Why?”

Other Jonas heaves a heavy sigh, as though explaining this to a child. “Because by that point you’ll only have one reality-slip left. Two minus one is one, right? You’ll be down to one last untethering, and you’re not going to want to waste it.” Jonas shoots him a look. Elaborate. “Right now, every cell in your body is working to expel the quantum radiation you’ve loaded them up with. Moving between realities speeds up that process. Remember the battery? You can’t replace it, but you can give it one last—brief—jolt by topping it off.”

“With a particle collider.”