“I killed you!” Other Jonas is screaming, his voice disturbingly familiar. “I killed you! How can you be alive? I killed you!”

His foot sails again—this time toward Jonas’s head—but Jonas catches it. Gripping the sole of Other Jonas’s shoe with both hands, he twists hard to the left until he hears a faint crack.

Other Jonas wails in agony and falls back. Jonas staggers to his feet. His chest is on fire, but he doesn’t think any ribs are broken. He chances turning his back to Other Jonas so he can lurch back toward the closet.

In seconds, Other Jonas is on the attack again with a guttural roar in Jonas’s voice, but it is a sound Jonas could never envision himself making, even at the nadir of despair over Amanda’s death. Other Jonas is almost atop him, but Jonas now has one of the closet’s wayward floorboards in his hands. He swings it hard and is rewarded with the sickening sound of wood against skull.

Other Jonas drops to the floor at the outer edge of the closet. Out cold.

Jonas stares at this other man, studying him. Fingernails long, dirty. Clothes disheveled. Face gaunt. Familiar, but a stranger. A chilling fun-house mirror.

Jonas staggers toward the nightstand. He bends to retrieve the fallen picture of Amanda. But the glass is cracked, right across her face. He removes the photo from the fractured frame and runs a finger across Amanda’s face.

Wishing it were the real thing.

Other Jonas lies unconscious on the floor. His head is bleeding from where Jonas struck him, but even if he were in pristine condition, he would still strike Jonas as pitiable. He is noticeably thinner, making him seem strangely older in appearance than Jonas. His skin is pale but for the smudge of unkempt stubble. His hair is wild and greasy.

Jonas studies this strange intruder. Maybe he isn’t an intruder at all. Maybe this is his apartment. If so, who is the Jonas beneath the floorboards? What parallel reality does he hail from? Jonas’s world cantilevers with questions as the most pressing one springs forth: What will he do next?

Jonas watches as Other Jonas stirs awake. At first, his movements are lolling, passive. A slow transit back to consciousness. Once awake, his eyes fly open. His head snaps forward. He jerks and discovers the torn bedsheets that have been repurposed to confine him.

Waking has done little to improve his appearance. He still resembles a shadow of Jonas, a desaturated version of himself. In the days following Amanda’s death, Jonas imagines he might have appeared as pathetic. But only barely.

He sits opposite his twin. The two dining room chairs he’s moved into the bedroom oppose each other like a reflection. The only difference is the men sitting in them. One is bound, the other is not. One has a bandage on his head, the other is uninjured, despite what the protestations inside his skull have to say on the matter.

Jonas is relieved to see that the mania has left his counterpart, leaving a detached confusion in its wake. Other Jonas lolls his head from side to side. Jonas lets him take as much time as he needs to orient himself. He needs his doppelgänger as lucid as possible, which, Jonas reminds himself, might be a heavy lift.

Eventually, Other Jonas focuses. He appears as unnerved by the sight of Jonas as Jonas was by the sight of him. Jonas has no idea what’s going on behind those all-too-familiar eyes. The opaqueness of his twin’s thoughts is disquieting.

Having gotten Other Jonas’s attention, he begins with gallows humor. “Hi. Nice to meet me.”

Other Jonas doesn’t react. He’s too busy staring at Jonas in disbelief. “I killed you,” he says with utter conviction.

Between bandaging Other Jonas’s head, moving in the chairs, stripping the bed, tearing the bedsheets, heaving Other Jonas onto one of the chairs, and tying him to it, Jonas had plenty of time to reflect on what may have happened. “You returned to the apartment,” Jonas says, reconstructing the past hour. “You saw the floorboards. The crawl space. You saw me. And, what, you thought I was him?” He glances back in the direction of the closet, toward the final resting place of the third Jonas. “Somehow risen from the dead?”

“I haven’t been at my most lucid recently, I’ll admit.”

Hearing his own voice respond, complete with his familiar syntax and inflections, is unnerving in the extreme. So is the fact that Victor didn’t kill the Jonas lying beneath the floorboards. That Jonas was killed by the one he was staring at right now.

“Trying to murder yourself,” Jonas says, “your other self, is a little more than just a lack of lucidity.”

Other Jonas’s head offers a shallow bob. A hint of a shrug. A halfhearted admission.

Then Jonas asks the question that is forefront in his mind. “Which one are you?” Other Jonas seems confused. “You or the other one. Which one is . . . ?” He stops, realizing he doesn’t know quite how to put the question.

Other Jonas does. “You mean ‘Jonas Prime?’” he asks, amused by the question. “The Jonas Cullen—the us—of this reality?” He cocks his head and gives a look of pity ordinarily reserved for funerals. “Does it matter?”

“Indulge me.”

“Him. This is . . .” He stops and corrects himself. “This was his reality.”

“Why’d you kill him?” Jonas asks.

Other Jonas chuckles. Everything is amusing to the mad. “Guess this world just wasn’t big enough for the two of us.” He laughs at his own joke.

“This isn’t funny.”

“Amanda always said I was my own worst enemy.” Another joke. Like a borscht belt comic. I’ve got a million of ’em, folks. “It’s like a riddle. When is killing yourself not suicide?”

“I think the better question is why do it in the first place?” Jonas feels the back of his neck beginning to warm and tastes bile in his mouth—he’s starting to lose his patience.

Other Jonas eyes the closet, its doors still open, the crawl space still gaping. His familiar voice grows distant, his tone stripped of affect. “He was trying to stop me.”

“Stop you from doing what?”

“From making the calculations. From finding Amanda.” All evidence of humor vanishes, and Other Jonas becomes deadly serious, his voice laced with an echo of his earlier desperation. “I couldn’t let him institutionalize me.”

Jonas pushes down a pang of queasiness and asks, “Why was he trying to stop you?”

Other Jonas flashes confusion again. “Isn’t it obvious?”

“Let’s pretend it’s not.”

“He thought I’d ‘break’ the multiverse. He thought I was obsessive. I suppose I am.” Other Jonas stares a hole into Jonas. “And before you start judging, it looks like you are too.”

Jonas doesn’t debate the point. “When she died . . . the first time she died . . . I couldn’t leave here, this apartment. Could hardly get out of bed.”

Other Jonas nods, sharing the same painful memory.

“I knew she’d want me to move on,” Jonas says, “but I didn’t know how. So I made a bargain with myself . . .”

“One hour at a time, one day at a time,” Other Jonas says, knowing the mantra.

“Don’t look back, just keep moving forward,” Jonas responds.

Other Jonas stares at him like a curio mounted behind glass, an exotic specimen. “You said the ‘first time’ she died . . .”

Jonas adopts the tone of a penitent in a confessional. “I found her. The one universe where she’s still alive. Or was,” he corrects himself, his voice catching in his throat. “And I lost her again.” The words come in barely a whisper.

“So why’d you come here?” Other Jonas asks. Jonas searches for a way to describe what he sees in his twin’s face. Is it . . . sympathy?

“I had to go somewhere.”

Other Jonas bobs his head at the simplicity of that. Perhaps he’d even made the same choice before insanity took him.

Jonas points to the equations running up and down the walls. “Are these yours or his?”