Teeth gritted against the pain, Jonas attempts to stand again. He moves slower this time and accomplishes the feat of toddling on watery legs. “I don’t want to speak with a psychologist.” He casts about for his clothes. “I just want to leave.”

“I think you and I both know that you’re in no condition to go anywhere.”

Ignoring that, Jonas considers the room. It’s empty, apart from some medical equipment, a chair, and a flat-screen mounted on the wall. “Where are my clothes?”

“You have a concussion—”

“Where are my clothes?”

“You really should get back in bed.”

Jonas would very much like to. His head feels light, and each breath brings a new volley of agony. Nevertheless, he surges toward the doctor. He doesn’t want to get violent, but he feels out of control, consumed by an overwhelming hunger to get out of this hospital. Once he’s out, he can think. He can orient himself. He can figure out his next move. He can see if she’s here, and if she is, he can find her. That’s all he cares about. Out of an infinite multitude, that’s the only reality that exists for him.

Covance Hospital is a thirty-five-minute drive from Eva Stamper’s office on a good day. On a bad day, when the narrow roads are clogged with traffic, it’s nearly an hour. Today is a bad day. And so Eva is in a mood. The hospital has a phalanx of psychiatrists and psychologists on staff, and even more on call. Paul Guyer must know that he’s taking advantage of their friendship by asking for her.

“An attempted suicide, I believe,” he had told her over the phone.

“So?” Eva rejoined. “You have people for that sort of thing. Good people.”

“I know, but . . .” And then his voice trailed off.

“But what?” Eva had asked, almost immediately chiding herself for taking the bait.

“There’s something different about this one.”

“Different how?”

“He has a tattoo on his inner forearm, to start.” Eva remembers rolling her eyes. “I’ve never seen anything like it.”

“What type of tattoo?” she asked, knowing that with every question, she was inserting herself deeper into a situation she wanted no part of. No, that wasn’t it exactly. It was that she had no time. She had patients enough of her own without taking on one of Paul’s pet projects.

“It looks like a formula of some kind,” he had explained. “An equation, I guess you could say. I don’t know. It doesn’t resemble anything I saw in medical school. But it’s odd.”

“That’s not a good enough reason to cancel on my patients and come down there in the middle of the day.”

“It’s barely ten in the morning.”

“You know what I mean, Paul.”

Although Paul is thirty years her senior, they’d always enjoyed a close relationship that skulked just up to the line of romance. One drunken evening, months after her husband’s passing, Eva had made a clumsy attempt at crossing that bright line, but Paul was kind and respectful as he gently rebuffed her. In another life, another universe, they might be lovers. The fact isn’t lost on either of them, and it makes for an unexpectedly strong bond. “The truth is, Eva,” he had said on the phone with a hint of mischief, “you’re looking at this the wrong way.”

Then it had been Eva’s turn to smirk. “And how’s that?”

“I could be the one doing you the favor. You could get a paper out of this,” he dangled.

“You say that every time, you shit,” she shot back lovingly. “And never once has it ended up being true.” Then they both enjoyed a good laugh.

And so she finds herself at Covance. Paul has arranged visitor parking for her. She navigates the corridors from memory and has to acknowledge that she’s been here too many times, seen too many of Paul’s patients “as a favor,” and not for the first time, she questions why Paul feels the need to call on her in this way. Or why she lets him.

But when she enters the patient’s room, everything changes. She feels like the victim of a prank. The world doesn’t make sense.

“What is this?” she asks.

Paul shoots her a quizzical look as Eva studies the patient. He’s a man in his thirties, somewhat on the thin side. His black hair is cut short, almost military length. He wears black jeans, and she can see the tattoo Paul mentioned as the man pulls on a black T-shirt. Her attention ping-pongs between the tattoo and the man’s face. She tries to make sense of what she’s seeing, but her best attempts bring her back to the suspicion that Paul is having some fun at her expense. He must have hired an actor, some kind of impersonator. Still, she can’t fathom why Paul would prank her like this. It’s too random. Too specific.

“What’s going on here?” Eva finally asks.

“What are you talking about?” Paul replies. He seems just as confused as she is. If it’s a performance, it’s a good one.

Eva returns her attention to the man, feeling him watching her. She points to him and asserts with as much conviction as she can muster, “This man is dead.”

“What?”

“Do you know who he is?” she presses, gesturing in the patient’s direction.

“H—he told me his name is Jonas,” Paul stammers.

The name is eerie confirmation of the evidence before her eyes. “Yes,” she whispers, her throat dry. “His name is Jonas Cullen.” The man startles, his face registering shock at being recognized. “Two years ago, he and his wife were killed in a car accident.”

Paul blanches. The man claiming to be Jonas Cullen appears staggered, almost doubled over with what seems like grief.

“She’s not here,” he whispers, his voice cracking with a hollowness she finds heartbreaking. “She’s not here,” the man says again, with greater conviction but no less dolor.

“What are you talking about?” Paul asks him. “Who is ‘she’? Who are you?”

Eva watches the man, this Cullen look-alike, as he drops into a chair. She knows the emptiness in his eyes. It’s the same emptiness that was in hers when she waited to hear whether her husband had been killed—a strange amalgam of lost hope and the bitter realization that hope was futile in the first place. “Can I have a minute alone with him, Paul?”

Once Paul leaves the room, Eva searches the recesses of her mind for traces of those years she spent studying physics. Equations in the stranger’s tattoo tug on her memory. She tries to piece together what she knows. Jonas Cullen isn’t dead. He’s right in front of her, as real as anything she’s ever known. But his wife is dead, and he appears to be . . . surprised at that? Eva plays with these disparate thoughts. It’s like a puzzle, but one where the pieces don’t fit . . .

“How do you know who I am?” he says. His voice rises barely above a whisper.

Eva shrugs. “I read about the accident on Google News last week.”

“Last week? Not two years ago?”

“Last week. Tragedies have a way of”—she strains for the right words—“of making an impression on me. Your wife was pregnant, wasn’t she?”

The man droops in the chair, nodding as though the effort to do so exhausts him. He seems utterly lost, his eyes devoid of life. Eva’s seen eyes like that before, in hundreds of hopeless patients: despairing.

She expects him to start crying, but he doesn’t. She has the sense that all his tears have been spent. “The formulae on your arm,” she ventures. “I’ve seen some of them somewhere before. At university. That’s a Schrödinger equation, isn’t it?”

She’s rewarded with a hint of recognition. “That’s right,” he says, slowly emerging from his fog. “What do you remember from your university days?” The words come out with the croak of effort.

Eva bends to study the formulae, trying to disregard the letters and symbols she doesn’t understand, working to excavate the Schrödinger equation from both the tattoo and her memory. She can feel the man watching her think. She senses that she’s stumbling toward the truth, a marathoner straining in the final inches to cross the finish line.

“It’s a linear partial differential equation,” she breathes. “It describes the state function of a quantum-mechanical system.” Her thoughts begin to gather momentum and form, like a snowball rolling downhill, picking up mass and speed. “The reason you’re here, and your wife isn’t . . .” She stops, not yet ready to say it out loud.