Three divisional directors sat to the left. Two senior analysts sat to the right, notebooks open. A systems engineer Isaac didn't recognize sat at the far end with a laptop. The projection screen showed a portfolio allocation model. Isaac had seen such models before.

He had built such models before in another version of his life, at a firm four blocks away where he had worked 80-hour weeks and had been, by most measures, extremely good at it. He moved along the wall, setting cups at each station, maintaining the practiced invisibility that the role required. He did not rush. He did not draw attention. He worked from right to left, and when he reached the end of the table nearest the screen, he stopped.

Not because he intended to, because the numbers he was looking at would not let him keep moving. The correlation matrix in the upper right quadrant of the model. The coefficient values. The baseline date range annotated in the footnote at the bottom of the slide. He read them in less than 3 seconds, the way someone who has spent years reading such things reads them without effort, without transition, directly into understanding.

The model was using historical correlation data from a period of low market volatility, a standard stable window, clean data. The kind of window you would use if the current market conditions matched that profile. They did not. In the past 48 hours, volatility had crossed the threshold. The entire risk calibration would misfire.

The automated rebalancing sequence would trigger a cascading series of sell orders in the wrong direction across at least four major positions. The estimated floor of the loss, given current conditions, was somewhere between 80 and 95 million dollars, and that was assuming the market moved cooperatively in the first 30 minutes. Isaac stood at the end of the table with an empty tray in his hands. He was still calculating the second scenario when Diana Callaway turned her head and saw him. She looked at him the way people look at furniture that has been left in an inconvenient place.

Not with hostility, exactly, but with a particular species of impatience that does not require a reason. "You're done here," she said, not unkindly, not cruelly, simply with the tone of someone stating an obvious fact to an entity that should have already understood it. You just make coffee. Your job is done. You can go."

A few people at the table glanced up. Adrian's laser pointer continued its orbit across the screen. The systems engineer did not look up from his laptop. Isaac looked at Diana for one moment. He looked at the screen one more time, then he nodded, gathered the empty cups onto the tray, and walked to the door.

The click of the latch behind him was the loudest sound in the hallway. He stood there for a moment, the cart beside him, the hum of the building's ventilation system filling the space where a decision had not yet been made. He had been in rooms like this. He had built things like that model. He had learned in the years since he had left that world not to carry what he used to carry, the weight of other people's numbers, the obligation of other people's problems.

He had made a deliberate choice to put down those tools, not because he could not lift them, but because what he was choosing to carry instead, a yellow duck mug, a spiral notebook, a promise about 3:00, was worth more. But $90 was not an abstraction. It was a real number. It would fall on real people. He pushed the cart toward the elevator.

And in his jacket pocket, he opened the notebook to a fresh page. He picked Luna up at 3:00, as promised. She ran out through the school gate with her backpack bouncing and her hair in a condition that suggested the wind had been involved at some point. She thrust a drawing at him before she had fully stopped moving, a crayon illustration of three figures standing in front of a building that might have been their apartment or might have been a castle. It was hard to be certain.

Two tall figures and one small one. "That's us," she explained. "And that's Biscuit. Who's the third tall one?" Luna considered this.

"That's also you, from the future, with a hat." He studied the drawing as they walked to the bus stop. Future Isaac appeared to be wearing what might have been a sombrero. On the bus ride home, Luna fell asleep against his arm before they had gone four stops. He sat still and let her sleep.

And through the window, watched the city pass, the movement and noise of it, the restless arithmetic of its streets, and thought about a set of numbers on a projection screen that he had no obligation to think about. He thought about them anyway. After dinner, after Luna's bath, after the third reading of a picture book about a hedgehog who kept losing his mittens, after the lights in her room were out and biscuit was positioned correctly on the pillow, Isaac sat down at the kitchen table. He opened the notebook. He worked from memory, which had always been reliable for this kind of material, reconstructing the model parameters he had read in the conference room.

It did not take long. The structure of these models was not novel. He had worked with variants of it for 7 years before Luna was born and his wife was alive and his life had a completely different shape. He laid out the correlation matrix the way he had seen it on the screen. Then he laid out the current market conditions beside it.

Then he connected the two with the logic of the rebalancing algorithm and watched where it broke. It broke where he had expected it to break. The coefficient for mean reversion had been hard-coded against a volatility regime that no longer matched the environment. In a standard session, the algorithm would scan, calibrate, execute, but the calibration step had a flaw, not in its logic, in its reference point. It was like using last winter's map to navigate a city that had been rerouted since spring.

The code that needed changing was almost certainly three lines, possibly four. The fix itself would take someone familiar with the system approximately 20 minutes, assuming they knew where to look. Isaac wrote out the corrected version of the correlation input on the bottom half of the page, checked it twice, then sat back. He looked at the drawing on the refrigerator. Luna and two versions of him and biscuit standing in front of a building that might have been a castle.

The future. Isaac in the sombrero had an expression that was hard to read at this scale, but seemed possibly content. Isaac thought about what kind of man he wanted to be in that drawing, not for anyone watching. There was no one watching. He thought about it for himself, which was the only way the question had ever made real sense.

He picked up his phone. He had Giselle Park's number from a handful of prior catering coordination calls. He scrolled to it and typed a message. This is Isaac Vain, third floor coffee station. I need to speak with whoever is responsible for tomorrow's trading session.

I believe there is a critical problem with the risk model. I think this is urgent. He read it over, added nothing, sent it. He set the phone on the table and looked at it for a moment, then looked at the notebook instead. On the inside front cover, in handwriting that was a little different from his current handwriting, tighter, pressed harder into the paper, there was a line he had written 5 years ago, in the months after the accident, when he had needed reminders for things that should not have required reminding, do the right thing even when no one is looking.

He closed the notebook. He went to bed. He did not sleep much. He arrived at Vantage Capital at 6:45, a full hour before his shift began. He went to the lobby desk instead of the staff entrance.