Chloe Vance had built a machine to solve a problem she could not solve any other way, which was the problem of being a person.

It had taken her three weeks. It sat now on a workbench in the corner of the library's little-used study annex - she'd commandeered the space; nobody else wanted it - a tangle of sensors and circuit boards and a central display, the most ambitious thing she'd ever made and, by some distance, the most ridiculous, though she would have defended its scientific rigor to her last breath. She called it, in her private notes, the Interpersonal Compatibility Assessment Apparatus. She called it, in her head, where she was honest, the thing that might tell me whether I have a chance.

The logic, to Chloe, was impeccable. The problem with Leo - the problem with the whole catastrophic situation - was uncertainty. She didn't know whether what she felt was reciprocated. She didn't know whether they were, in any meaningful sense, suited. She didn't know how to find out the way other people apparently found out, through conversation and intuition and the reading of signals she could not read, and the not-knowing was unbearable, a variable she couldn't pin down, a question with no data. So she had done the only thing she knew how to do with an unbearable unknown. She had built an instrument to measure it.

The Apparatus measured physiological synchrony - heart rate coherence, galvanic response, micro-expressions, a dozen subtle signals - between two people, and computed from them a compatibility index. It was, Chloe believed with the fierce conviction of someone who needed it to be true, real science. It was also, she knew in the honest place, an elaborate excuse to sit very close to Leo Evans for a sustained period with a legitimate reason to hold his hand for the sensors, and she had decided not to examine that second thing too closely.

She ambushed him in the garden, which she'd discovered was where he went now - she'd run the correlation, same as the others, and found him.

"Leo," she said, appearing at the edge of the plot with the Apparatus in a wheeled case, going pink the moment he looked up. "I require - I have a thing. A device. I need a test subject and you're - statistically convenient. It won't take long. It's for science."

Leo, kneeling in the dirt, wiped his hands and smiled at her with the easy welcome he always had for her, the welcome that still slightly undid her every time. "Hey, Chloe. A device, yeah? Course. What's it do?"

And Chloe, who had prepared a careful obfuscating explanation, found it tangling on her tongue the way her words always tangled when he looked at her like she was someone worth looking at. "It - measures. Interpersonal. Physiological." The stutter caught at the front of the hard words. "S-synchrony. Between two p-people. To assess - compatibility. Of various - it's a compatibility assessment. Apparatus. For research."

"Compatibility," Leo repeated, intrigued rather than suspicious, because of course he was. "Like, how well two people get along? You can measure that?"

"You can measure correlates of it," Chloe said, on firmer ground now that they were discussing methodology. "Heart rate coherence, primarily. When two people are - comfortable together, attuned, their physiological rhythms tend to synchronize. It's documented. I've refined the measurement." She set up the Apparatus on the garden table with brisk competent hands, the one part of all this she was genuinely good at, and gestured to the sensors. "I need a second subject. To establish whether the device functions. You can be the - you'd be helping. With the research."

"Sure," Leo said, settling onto the bench across from her. "Happy to help. What do I do?"

What he had to do, it transpired, was hold her hands.

Chloe had engineered this with a precision she was deeply ashamed of. The sensors required palm contact; the optimal configuration required the two subjects to sit close, facing each other, hands clasped across the table so the readings could synchronize. She explained this in the flattest, most clinical voice she could manage, as though prescribing a medical procedure, and Leo - trusting, oblivious, kind - simply held out his hands across the table, palms up, waiting.

Chloe looked at his open hands.

Then, with her heart already climbing toward the readings she'd recorded at dawn so many times, she put her hands in his.

His hands were warm. They were a little rough from the gardening, callused, dirt still faint in the creases no matter how he scrubbed, and they closed around hers gently, carefully, the way he did everything, and Chloe's entire nervous system lit up like a city at night, and the Apparatus, registering this faithfully, began at once to climb.

"Okay," she managed, staring fixedly at the display so she wouldn't have to look at his face eight inches from hers. "It's - taking baseline. Just. Stay still. And it'll - we answer some questions, while it reads. The questions are - they're calibration. They establish conversational synchrony. They're standardized."

They were not standardized. She'd written them herself, the night before, agonizing over each one.

"First question," Chloe read off her screen, her voice not quite steady. "What is a thing you want that you've never told anyone?"

Leo blinked. "That's a calibration question?"

"It measures - openness response," Chloe said, which was nonsense, and pressed on. "You don't have to - it's for the reading. Just answer honestly. The device detects honesty. Sort of."

And Leo, holding the hands of a girl he thought of as a friend, in a quiet garden, with no idea he was being gently interviewed by the most elaborate confession of feeling ever constructed, considered the question seriously, the way he considered everything she asked him, and answered it honestly, because she'd asked him to.

"A thing I want that I've never told anyone." He was quiet for a moment, his thumbs unconsciously, gently, resting over her knuckles, and Chloe watched the Apparatus and tried to breathe. "I guess - to belong somewhere. Properly. Like, I know everybody here treats me like I'm important, but it's - it's not the same as belonging, you know? They want the idea of me. The Charm, or whatever. Nobody actually - " He paused, and something honest and a little raw came into his voice, something he'd clearly never said aloud. "I've never really had a place where people knew the actual me and wanted me there anyway. Even before I came here. I was always kind of - background. The one nobody noticed. And now I'm the one everybody notices and it's somehow even lonelier, because they still don't see me, they just see - the rare thing." He gave a small embarrassed laugh. "Sorry. That's more than you asked. Your machine's gonna think I'm broken."

Chloe did not answer for a moment, because she couldn't.

Because she had built a machine to find out if a boy might be compatible with her, and the machine had instead just shown her his heart, and his heart was - she understood it with a vertiginous lurch - the same shape as hers. He was lonely in a room full of admirers. He was wanted for the wrong thing, the surface thing, the thing that wasn't really him, while the real him sat unseen underneath. He was The Charm the way she was The Genius - a label people loved instead of a person they knew - and he ached, exactly as she ached, to be wanted for the part of him that no one bothered to look at.

She had thought, building this, that she was the strange lonely one and he was the effortless beloved one and the only question was whether she could possibly deserve him. And the machine, or rather his answer to it, had just told her something the machine could never have measured: that he was lonely too. That under the adoration he was as unseen and as starved for real recognition as she was. That they were not the genius and the prize. They were two people standing on opposite sides of the same loneliness, reaching.

"It doesn't think you're broken," Chloe said, very quietly, and for once there was no stutter, no jargon, no machine in her voice at all. "I think it thinks you're - " she stopped, frightened of the size of what she'd almost said. "The reading is very high," she finished instead, retreating, as she always retreated, into the data. "The - coherence. It's very high. Higher than I - the baseline is anomalously -"

The moment trembled there, the truth so close to the surface she could feel it pressing - she could have said it, could have set down the machine and the jargon and the safe clinical distance and simply said me too, I'm lonely the same way, I see you, the actual you, I've seen you since the library - and for one suspended second she almost did.

And then the old fear closed over it like water. Because to say it she would have to put down the instrument, step out from behind the data, stand in front of him as just Chloe, the human part, the part that wasn't brilliant, the part she'd spent sixteen years certain no one wanted - and risk finding out that he, like everyone, only liked the mind. The risk was too large. The drop was too far. She wasn't ready.

So she pulled her hands back - gently, on the pretext of adjusting the device - and the warmth of his palms left hers, and she hid, once more, in the work.

"The test is nearly complete," she said, her voice gone clinical again, the shutter back down. "I just need to - process the final reading."

"That was a good question, though," Leo said, watching her with a thoughtful kindness that she couldn't quite meet. "The one you asked me. Made me actually think." He tilted his head. "What about you? Same question. A thing you want that you've never told anyone?"

Chloe froze over the Apparatus.

The honest answer sat right there, enormous: you. To be seen the way you just let me see you. To be wanted for the part of me that isn't useful. To put this machine down and just - be a person, with you, without needing a reason.

"That's not - the protocol only requires one subject to answer," she said, faintly, fleeing into procedure. "For - statistical reasons."

Leo let it go, the way he always let things go, with a small accepting nod that somehow made it worse, because it was kind, because he never pushed, because he gave her exactly the room she'd asked for even when she could see he'd have listened if she'd dared to use it.

And Chloe Vance bent over her beautiful useless machine, her hands still warm where his had held them, and understood two things with total clarity. The first was that the device had worked perfectly, and that she was about to get a number that would either devastate her or terrify her. And the second - the larger one, the one no apparatus could have told her - was that the real test had never been the machine at all. The real test was whether she could ever be brave enough to do what Leo had just done so easily, sitting in the dirt holding a stranger's hands: simply tell the truth about what she wanted, undefended, and trust someone to want her anyway.

She wasn't there yet.

But she pressed the key to compute the final reading, and watched the Apparatus begin to resolve the number that would change everything - and braced herself, for better or worse, to find out exactly how compatible a machine thought she was with the loneliest boy she'd ever met.