It was the most chilling, deliberate thing Patrick had ever seen in his life.

He looked down at the bowl of ramen noodles he had cooked himself for dinner, and realized he’d lost his appetite. Setting it aside on a stack of old newspapers, he rewound the video and forced himself to watch it again.

When the phone rang, he picked it up, still distracted by the sight of Peter on his television screen. “Yeah.”

“Well, hello to you, too,” Nina Frost said.

He melted when he heard her voice; old habits died hard. “Sorry. I’m just in the middle of something.”

“I can imagine. It’s all over the news. How are you holding up?”

“Oh, you know,” he said, when what he really meant was that he was not sleeping at night; that he saw the faces of the dead whenever he closed his eyes; that his mouth was full of the questions he was certain he’d forgotten to ask.

“Patrick,” she said, because she was his oldest friend and because she knew him better than anyone, including himself, “don’t blame yourself.”

He bent his head. “It happened in my town. How can’t I?”

“If you had a videophone, I’d be able to tell if you’re wearing your hair shirt or your cape and boots,” Nina said.

“It’s not funny.”

“No, it’s not,” she agreed. “But you must know it’s a slam dunk at trial. You have, what? A thousand witnesses?”

“Something like that.”

Nina grew quiet. Patrick did not have to explain to her-a woman who’d lived with regret as a constant companion-that convicting Peter Houghton was not enough. For Patrick to lay this to rest, he’d have to understand why Peter had done this in the first place.

So that he could keep it from happening again.

From an FBI investigatory report, published by special agents in charge of examining school shootings around the globe:

Among school shooters, we have seen a similarity of family dynamics. Often the shooter will have a turbulent relationship with his parents, or will have parents who accept pathological behavior. There is a lack of intimacy within the family. There are no limits for television or computer use imposed on the shooter, and sometimes there is access to weapons.

Within the school environment, wefound a tendency toward detachment from the learning process on the part of the shooter. The school itself tended to tolerate disrespectful behavior, exhibited inequitable discipline and an inflexible culture-with certain students enjoying prestige given to them by teachers and staff.

Shooters are more likely to have access to violent movies, television, and video games; to use drugs and alcohol; to have a peer group that exists outside of school and supports their behavior.

In addition, prior to a violent act, there is evidence of leakage-aclue that something is coming. These hints might take the form of poems, writings, drawings, Internet posts, or threats made in person or in absentia.

In spite of the commonalities described within, we caution the use of this report to create a checklist that might predict future school shooters. In the hands of the media, this might result in labeling many nonviolent students as potentially lethal. In fact, a great many adolescents who will never commit violent acts will show some of the traits on the list.

Lewis Houghton was a creature of habit. Every morning, he woke up at 5:35 and went for a run on the treadmill in the basement. He showered and he ate a bowl of cornflakes while he scanned the headlines in the paper. He wore the same overcoat, no matter how cold or hot the weather, and he parked in the same spot in the faculty lot.

He’d once tried to mathematically figure the effect of routine on happiness, but there was an interesting twist to the calculation: The measure of joy brought by the familiar was amplified or reduced by the individual’s resistance to change. Or-as Lacy would have said, English, Lewis-for every person like himself who liked the worn grooves of the familiar, there was another person who found it stifling. In those cases, the comfort quotient became a negative number, and doing what came habitually actually detracted from happiness. It was that way, he supposed, for Lacy, who wandered around the house as if she’d never seen it before, who couldn’t stand the thought of going back to her practice. How can you expect me to think of someone else’s child right now? she had argued.

She kept insisting that they needed to do something, but Lewis didn’t know what that was supposed to be. And because he couldn’t comfort either his wife or his son, Lewis decided he was left to comfort himself. After sitting at home for five days after Peter’s arraignment, one morning he woke up and packed his briefcase, ate his cornflakes, read the paper, and headed off to work.

He was thinking of the equation for happiness as he headed to the office. One of the tenets of his breakthrough-H = R/E, or happiness equals reality divided by expectation-was based on the universal truth that you always had some expectation for what was to come. In other words, E was always a real number, since you could not divide by zero. But recently, he wondered about the truth of that. Math could only take a man so far. In the middle of the night, when he was wide awake and staring up at the ceiling, knowing that his wife lay beside him pretending to be asleep and doing the very same thing, Lewis had come to believe that you might be conditioned to expect absolutely nothing from one’s life. That way, when you lost your first son, you didn’t grieve. When your second son was jailed for a massacre, you were not shattered. You could divide by zero; it felt like a canyon where your heart used to be.

As soon as he set foot on the campus, Lewis felt better. Here, he was not the father of the shooter and never had been. He was Lewis Houghton, professor of economics. Here, he was still at the top of his game; he didn’t have to look at the body of his research and wonder at what point it had begun to unravel.

Lewis had just pulled a sheaf of papers out of his briefcase that morning when the chair of the econ department poked his head through the open doorway. Hugh Macquarie was a big man-Huge Andhairy is what the college students called him behind his back-who had taken over the position with gusto. “Houghton? What are you doing here?”

“Last I checked, the college was still paying me to work,” Lewis said, trying to make a joke. He couldn’t make jokes, never had been able to do so. His timing was off; he gave away punch lines by accident.

Hugh walked into the room. “My God, Lewis, I don’t know what to say.” He hesitated.

Lewis didn’t blame Hugh. He barely knew what to say himself. There were Hallmark cards for bereavement, for loss of a beloved pet, for getting laid off from a job, but no one seemed to have the right words of comfort for someone whose son had just killed ten people.

“I thought about calling you at home. Lisa even wanted to bring a casserole or something. How’s Lacy holding up?”

Lewis pushed his glasses higher on the bridge of his nose. “Oh,” he said. “You know. We’re trying to keep things as normal as possible.”

When he said this, he pictured his life as a graph. Normal was a line that stretched on and on, teasing its way closer to an axis but never really reaching it.

Hugh sat down in the chair across from Lewis’s desk-the same chair that was sometimes filled by a student who needed a tutorial in microeconomics. “Lewis, take some time off,” he said.

“Thanks, Hugh. I appreciate that.” Lewis glanced at an equation on the far blackboard that he’d been puzzling out. “Right now, though, I really need to be here. It keeps me from thinking about being there.” Reaching for some chalk, Lewis began to print across the board, a long and lovely stream of numbers that calmed him inside.