He ventures out of the living room to explore the rest of the apartment, still holding the framed photograph of Amanda in Central Park like a talisman. The hallways are lined with towers of books on physics and quantum mechanics. The kitchen is a war zone where a battle appears to have been fought by frozen food containers and bottles of liquor. The dining room, in contrast, remains pristine, suggesting that no one has used the space in months, if not years.

He leaves the bedroom for last. If any room were to remind him of his marriage, it would be that one. So perhaps it’s a blessing that it’s also the most altered room in the entire apartment. The bay windows are covered, but not by blinds or curtains. Closer inspection reveals the window coverings have been replaced with black trash bags. Their effect is to blot out even moonlight and the city’s nighttime luminescence. He fumbles in the dark for the light switch, which he discovers is conveniently located on the same wall as in his universe.

The light reveals a room he does not recognize. The wallpaper has been painted over in white, every inch covered top to bottom with exotic formulae reminiscent of his tattoo but rendered in a madman’s scrawl. Those patches of wall not covered with equations hold taped-up pages, articles and diagrams torn out of scientific journals and newspapers and magazines—an obscene collage.

The sight brings a queasy sensation. The arcane formulae with their ragged, urgent writing suggest a man who fell headfirst into a pit of grief and continued to plummet until he hit madness. The torn pages shriek with a wild desperation, a wretched search for theoretical ephemera.

On the nightstand, Jonas finds a sheaf of papers piled almost high enough to topple. Some instinct compels him to sit on the bed—its sheets unwashed—and pick up the stack. He shuffles through the papers, his fingers quivering. His stomach nose-dives at the sight of a laser-printed email confirming the payout on a life insurance policy. Jonas and his Amanda had taken out a similar one at the suggestion of some financial planner. He studies the email, and it confirms his dark instinct that this universe’s Amanda is gone.

In this world, there is no Nobel, no heady night in Stockholm, no adoring crowd at the Aula Magna. Nor is there an ill-fated drive over the Centralbron. Yet Amanda is just as dead. Reams of paper from car-insurance companies and the New York Department of Transportation and the New York City Taxi and Limousine Commission tell the story: Jonas’s Prius was struck by a taxi, which leaped a broken guardrail on the FDR Drive. Jonas reads conflicting denials of responsibility and varying offers of settlement. Polite entreaties for Jonas to refer the cab company’s lawyers to his. Pleas for him to answer emails and other correspondence. Despite the players being different, the documents are eerily like those Jonas ignored in his home reality. Cards and printed emails of sympathy and condolence. He couldn’t bring himself to read them before and feels no such compulsion to do so now. No words could console him, and he had no friends whose attempts at consolation he cared to endure. Without Amanda, the world was empty, as bleak and stark as the moon. An ocean of sympathy couldn’t quench the desert of his soul.

The papers and letters and emails form a fossil record that documents the months of grief he remembers enduring. But eventually he sees a break in the strata, a point where his doppelgänger’s life begins to diverge from his own. Instead of going away quietly, the correspondence from friends and colleagues grows more worried. Their emails having gone unanswered, some take the trouble to write letters, each expressing mounting concern for the mental health of Jonas’s counterpart.

In this reality, Victor made no claims of plagiarism. No review into jealous allegations was conducted. No tribunals were convened. This universe’s Jonas held on to his position at Columbia University.

But then Amanda died. The bulk of the papers at the bedside is dedicated to a litany of complaints submitted to the physics department, revealing a tableau of wild outbursts in class on those rare instances when Other Jonas attended. There are reports from concerned students and teaching assistants who were watching their professor unravel.

In the pages, Dorothy Stanton volleys a series of requests that Jonas undergo a psychological evaluation. Over time, the requests morph into demands. The demands become reluctant threats. The coup de grâce is a letter terminating his employment. By this point in the epistolary narrative, it comes as a mercy.

All told, the papers tell a story of a grieving widower’s coming undone, his eventual professional banishment and ostracism. Jonas sets them back down on the nightstand, feeling that he’s committed an invasion of privacy, but then he’s tempted by the bedroom closet, its door hanging open like an invitation.

Jonas pads inside. Shirts and slacks and pants hang over a floor littered with discarded items of clothing. Jonas considers his own wardrobe, dirty and probably smelling almost as bad as this apartment. Surely there are items with all-natural fibers here, and he’s reasonably confident they’ll be his size.

He flicks the closet light on and begins searching for a change of clothes. Out of habit, he scans for items that would reality-slip with him before realizing that he has no intention of leaving the universe he now occupies. Without hope of finding Amanda, he has nowhere else to go. In any universe. True, he could travel. The first pioneer of the multiverse. He could explore and document. He could publish in thousands of realities, collect Nobels in every universe. But what would be the point? Amanda would still be gone. An infinite collection of honors and laurels would not bring her back. Life would remain hollow. Colorless.

As he skulks through the closet, he feels something shift beneath his feet, just a slight give accompanied by a quiet creak. He nudges aside a small pile of laundry to excavate more of the floor and tests the floorboard with a tap of his shoe. It buckles slightly.

Jonas remembers the stench. He’d grown almost nose-blind to it, but it’s more prominent in the closet. He descends to a knee and runs his fingers over the floorboard’s edges. He pushes down with his other hand, and the wood seesaws up slightly, giving him more to grip. Lifting it out unleashes a new volley of fetid air, confirming his suspicion. He swallows hard against the impulse to gag and removes the other floorboards, exposing a narrow crawl space.

Jonas lowers himself down. His feet dangle, dropping inches before touching solid ground. Concrete, maybe? The channel is small and dank. Without enough room to stand, he crawls on his hands and knees. Cobwebs ensnare his face. A cockroach skitters near his hands. The stench is like a wall, and he forces himself to breathe only through his mouth. But this approach offers scant help, and he fights the urge to vomit.

Once his vision adjusts, he can make out a shape in the darkness ahead of him, black with a subtle sheen to it, evoking the image of an insect’s carapace. A distorted lump is shoved into the maw of the crawl space, and closer inspection reveals that the patina catching the half light is some kind of plastic.

More garbage bags.

Beige masking tape coils around the bags, tightening around their contents and segmenting them into—

Jonas pales. Fear grips him.

What at first appeared misshapen now takes form. A human form.

Jonas’s terror ratchets up, but it’s overshadowed by a compelling need to confirm the bags’ contents. He claws away at them with the urgency of a child opening presents on Christmas morning. The plastic stretches, frustrating his efforts. With growing exigency, he pulls and tears at the ebony cocoon, digging his nails into the plastic. Eventually it gives, and he’s assaulted by the smell that emanates. He continues to peel away the plastic until even in the darkness he can see it.

A human corpse.

Jonas can just make out the face staring back at him with lifeless eyes. He knows it well. He’s known it all his life.

It’s his own.

NOW

Four hours, three drinks, and half a Xanax after shooting Amanda Cullen, Victor Kovacevic still can’t stop his hand from shaking. Here in the palatial kitchen of his equally palatial Manhattan apartment, ten blocks and an entire universe away from the one in which Jonas is staring at a corpse with his own face, the gun rests on the bar top. Sitting on a stool, Victor stares at it. A Smith & Wesson M&P 9 Shield. Lying on the marble right next to his fourth glass of Macallan 18. The gun is a compact little thing, weighing just slightly over a pound, wrought of stainless steel, synthetic rubber, and a proprietary polymer. He bought it online for less than four hundred dollars.

The gun holds a total of eight bullets, and it’s only been fired once. The Macon that Victor hired told him he didn’t even have to practice. Just point and squeeze, the mercenary had said. Most TV remotes are harder to operate.

Macon would have been happy to do it himself, of course. The man had pulled triggers for far less than the twenty-five thousand dollars Victor was paying him. But Victor wanted to do the deed himself.

He picks it up and, not for the first time, marvels that the weapon has traveled to another reality and back. Jonas’s method wouldn’t permit it, but the transportation of nonorganic materials is just one of the many ways Victor has proved his skills to be superior to those of his nemesis.

But when he sees the ruddy fleck of Amanda’s blood on his hand, he sets the gun down. He tries to scratch it off with a fingernail, but it persists. He thought he’d removed all the blood hours ago. He moves to the kitchen sink and washes, still unnerved by the sight of her spatter on his face in his bathroom mirror. Driven by the memory, he scrubs even harder now.

Out, damned spot; out, I say!

His right hand is still shaking, so with his left, he reaches out and drains the scotch. He has no idea why his hand should tremble, much less four hours after the deed. It was the right thing to do. The necessary thing. The thing he felt, in his bones, that the universe wanted him to do. And now it is done.

And his hand. Is. Still. Shaking.

He balls it into a fist, but still it quivers. Deciding that he needs to get his mind off Amanda, the image of her abdomen erupting with blood, Victor moves to the guest room, where the Cray XC30-AC supercomputer resides. Four towers, each the size of a refrigerator, dominate the room. Victor pours himself into the chair in front of his workstation and commands the computer out of its sleep cycle. It cost him $500,000, and Victor is once again thankful that Phaedra came from money.

His fingers fly along the keyboard. The usual commands cascade down the flat-screen monitor. The data reminds him of a waterfall. The Cray throws off a lot of heat in its labors, and Victor opens a window to let in the night air.

He questions why he’s running the program again. The algorithm searches the multiverse for the quarks and neutrinos thrown off by Jonas’s tether, like a magnet that pulls the needle from an unbounded number of haystacks.

But why? Amanda’s dead. The scales of karma—of justice—are balanced.

It’s over.

Yet he feels compelled to learn whether Jonas stayed behind. And if he did leave that reality, where did he travel next?

And why does it matter?

It’s over.

The answer, of course, is the same reason his hand still shakes. The needs of the universe may be satisfied, but his—his—remain discontented. He was certain that Amanda’s death would do it, but a flicker remains lit within him. Hate.

It occurs to Victor that if he can locate Jonas by his tether’s emissions, it follows that he might be able to manipulate those emissions. Perhaps even disable the tether’s operation entirely. And in so doing, Victor would sentence Jonas to a life of passing between universes—from reality to reality to reality—in a relentless purgatory.

Damned by the same invention Jonas had stolen from him.

The symmetry is too perfect to ignore. Once again, Victor hears the call of the universe. Charged, he returns to the workstation, opens a new window, and begins coding a new algorithm. He saves the file as KARMA2.0, and as he types away, he’s hit by a realization.

His hand is no longer shaking.

FOUR YEARS AGO

The morning sun raked across their naked bodies, their limbs entwined like branches, basking together in their afterglow.

“Let’s stay like this forever,” Amanda said.