The first thing to understand about Leo Castellano is that he was not a bad man. He was, by every measure available to him, a good one. He returned his calls. He tipped well. He remembered his mother's birthday and sent flowers that arrived on the correct date. He had never cheated on a girlfriend, never stolen anything more significant than a hotel ashtray, and never deliberately caused anyone harm. When he moved into the second-floor apartment on Harper Avenue in West Hollywood in February of 1987, he introduced himself to every neighbor on his floor, left his phone number with the building manager, and made a mental note to learn the mail carrier's name. These were the rituals of decency as he understood them, and he performed them with the same conscientious attention he brought to his screenplays: structure, payoff, catharsis.

Rita moved into the apartment directly below his in March. Leo met her in the laundry room three days after her arrival, both of them sorting whites from colors at eight o'clock on a Wednesday morning, which in Hollywood meant neither of them had anywhere to be. She was twenty-six, he guessed, with the kind of face that casting directors described as interesting, which meant she was beautiful in a way that didn't photograph easily. She had moved from Ohio six months earlier and was waiting tables at a restaurant on Melrose while she went to auditions. Her boyfriend, a man named Derek whose primary occupation seemed to be managing Rita's career decisions, had found the apartment for her.

"He's very protective," Rita said, separating a red sock from a pile of towels. "He wants to make sure I don't get taken advantage of."

Leo nodded. He had been in Los Angeles long enough to understand that protective was a word that could mean many things, and that asking too many questions about someone else's protective boyfriend was not how you made friends in a new building. He loaded his whites into the washer, added detergent, and went back upstairs to work on the second act of a script that Paramount was paying him sixty thousand dollars to deliver by the end of the month. This was Threshold Zero: the moment before any decision was required, the baseline state of not-knowing that would later seem, in retrospect, like the last moment of innocence. He did not recognize it as such because the present never announces itself as the past.

Threshold One arrived in April. Leo was on page eighty-seven of his Paramount script, the part where the protagonist realizes his wife has been lying to him and must decide whether to confront her. The scene required raw emotional honesty, the kind of writing that demanded absolute concentration, and Leo had been attempting it since seven that morning when a sound from the floor below interrupted him. It was not a scream. Screams were identifiable. Screams had narrative function. This was something lower and more difficult to name: a muffled impact, followed by a voice raised and then abruptly lowered, as if someone had remembered that walls were thin and adjusted accordingly. Leo paused his typing. He listened. A door slammed. Footsteps in the hallway below. Silence.

He looked at his typewriter. The cursor blinked at him. He had seventeen pages to deliver by Friday and if he didn't deliver them, Paramount would hire someone else, and if Paramount hired someone else, his career would begin the long slow slide that careers in Hollywood were always, perpetually, one missed deadline away from beginning. This was the calculation he made, and it was a reasonable calculation, the kind of calculation that any reasonable person would make under the same circumstances. He told himself it was probably nothing — an argument, a slammed door, the normal friction of two people sharing a small space. He told himself that if it were something serious, someone else would hear it. There were six other apartments in the building. Wall Street had the whole month of April. He returned to his screenplay and did not think about it again, which is to say he thought about it for the next six hours.

This was Threshold One, and it was perfectly defensible. A writer on a deadline. An ambiguous sound. No visible evidence of harm. If you had asked Leo Castellano on that April morning whether he had just made a mistake, he would have said no, and he would have been telling the truth as he understood it, and you would have believed him, because the truth as he understood it was reasonable.

Threshold Two came three weeks later, on a Saturday afternoon in May. Leo was coming back from the farmer's market on Fairfax with a bag of avocados and a loaf of sourdough when he passed Rita in the lobby. She was wearing sunglasses, which was not unusual for Los Angeles in any month, and she was wearing long sleeves, which was slightly unusual for May but not unprecedented. Leo made a joke about hangovers, the kind of easy joke you make when you want to acknowledge that someone looks tired without actually asking them if they're tired. Rita laughed, or produced a sound that occupied the space where laughter would normally go, and said something about a late shift at the restaurant. They rode the elevator together. She got off at the first floor. He got off at the second.

In the solitude of his apartment, surrounded by avocados and the script for a romantic comedy that someone at Fox had described as When Harry Met Sally but with more car chases, Leo thought about Rita's sunglasses and her long sleeves and the sound that her laugh had almost but not quite been. He thought about these things for approximately ninety seconds, which was exactly long enough for him to construct three separate explanations for each observation and then dismiss all three as the paranoid overanalysis of a man who spent his professional life inventing conflicts and then resolving them. Screenwriters were trained to see stories everywhere. That didn't mean the stories were true. This was Threshold Two, and it was also defensible: a sighting in the lobby, a joke that landed slightly wrong, the paranoia of an overactive imagination.

Threshold Three arrived with the summer heat. Rita's agent, a man named Marty Gold who had once represented a minor star on a cancelled CBS drama and had been dining out on the association ever since, cornered Leo at a party in the Hills. The party was at a producer's house, the kind of party where everyone was someone or wanted to be someone and the difference between the two was visible only in the angle at which people held their drinks.

"Hey, you live in Rita's building, right?" Marty said, positioning himself between Leo and the bar. "She ever mention anything about Derek? Only she's been missing a lot of auditions lately and I'm starting to wonder if there's something going on."

Leo considered the question. He had never met Derek, had only seen him in the building's parking garage, a tall man with a gym membership and the kind of handshake that lasted half a second too long. He had no evidence of anything. He had suspicions, but suspicions were not evidence, and a party in the Hills was not a deposition, and Marty Gold was not a person to whom Leo owed anything more than professional courtesy. "She seems fine," Leo said. "Actors are flaky. You know how it is."

Marty nodded and moved toward the bar, and Leo spent the rest of the evening feeling the particular discomfort of a man who has just said something that was technically true and completely wrong. But it was true, wasn't it? Rita did seem fine. She paid her rent. She sorted her recycling. She waved when she saw him in the hallway. And actors were flaky — everyone in Hollywood knew that. Leo had not lied. He had simply chosen not to express a suspicion for which he had no concrete evidence, which was the responsible thing to do. This was Threshold Three, and any reasonable person would have done the same.

Threshold Four was the first one that required Leo to refuse something specific. It was August now, the worst of the Los Angeles summer, when the smog hung over the city like a dirty blanket and everyone who could afford to leave had already left. Rita appeared at Leo's door at ten o'clock on a Tuesday night. She was not wearing sunglasses this time, and in the yellow light of the hallway fixture Leo could see that her left eye was swollen in a way that makeup had attempted and failed to conceal.

"Could I crash on your couch tonight?" she asked. "Just tonight. There's some stuff going on."

Leo's girlfriend was over. Her name was Jennifer, she worked in development at Columbia, and she was currently asleep in his bed after an evening that had involved a bottle of Chardonnay and a long discussion about whether they should move in together. Leo thought about the logistics: the couch was not comfortable, Jennifer would have questions in the morning, the apartment was small and the walls were thin and the situation was clearly more complicated than Rita was admitting. He thought about all of these things, and then he said: "I'm sorry, Jen's here, it's just not a good night."

Rita nodded. She had been expecting this answer, Leo realized. She had come to his door already knowing that he would say no, and she had come anyway, which meant the question was not really a question. It was a test. It was the moment in the screenplay when the protagonist is offered a chance to be heroic and chooses not to be, and the audience understands that the choice will have consequences. But this was not a screenplay. This was a Tuesday night in August, and Leo had a girlfriend in his bed, and Rita's problems were not his problems, and that was not selfishness. That was boundaries. That was the healthy maintenance of personal space. This was Threshold Four, and it might have been the last fully defensible one.

Threshold Five happened in October, during what should have been the best week of Leo's career. The Paramount script had been greenlit. A major director was attached. Leo's agent was fielding calls from three different studios about his next project. He was on the phone with an executive at Warner Brothers, discussing numbers that would have seemed absurd to him two years earlier, when he heard the sound of glass breaking in the apartment below.

It was not a small sound. A wine glass, maybe, or a picture frame, something that shattered with theatrical finality. The executive on the phone was mid-sentence, and Leo had been waiting six weeks for this call, and he made a decision without even being aware that he was making one. He did not excuse himself from the call. He did not put down the phone. He did not go downstairs. He simply adjusted his grip on the receiver and listened to the executive talk about profit participation, and after approximately three minutes the sound from downstairs stopped, and by the time the call ended an hour later, Leo had convinced himself that it had been nothing more than a dropped glass, an accident, the kind of thing that happens all the time and means absolutely nothing.

This was Threshold Five, and its defensibility was beginning to fray at the edges. A dropped glass was plausible. A dropped glass during what sounded like an argument was slightly less plausible. A dropped glass during what sounded like an argument when the person dropping it had shown up at your door two months earlier with a swollen eye — that was a pattern, and patterns were the thing that screenwriters were supposed to be good at identifying.

Threshold Six came in late November, a week before Thanksgiving. Rita had told Leo she was visiting her parents in Ohio for the holiday. She had mentioned it in the elevator, making conversation about travel plans and family obligations and the price of plane tickets to the Midwest in November. Leo had wished her a happy Thanksgiving and had not thought about it again until he came home from a meeting on the Wednesday before the holiday and saw Derek's car parked in the building's garage. The same car. The same license plate. The same gym bag visible through the passenger window.

He stood in the garage for a long moment, considering his options. He could go upstairs and knock on Rita's door. He could ask Derek if Rita was home. He could call the police and report his suspicion that something was wrong. But what would he say? The woman in Apartment 1B had said she was going out of town, and now it appeared she had not, and also her boyfriend's car was here, and also there had been some ambiguous sounds over the past eight months. This was not a police report. This was not evidence. This was the accumulation of small observations that only made sense if you had been collecting them, and the only person who had been collecting them was Leo, and Leo was a screenwriter, not a detective. He went upstairs and made a sandwich and watched a VHS copy of The Terminator and went to sleep at eleven o'clock. This was Threshold Six.

Threshold Seven arrived without announcing itself. On the first Tuesday of December, Leo realized he had not heard any sound from Apartment 1B in three days. No footsteps. No music. No television. No voice. The silence was complete, the kind of silence that apartments produce when nobody is living in them anymore. Leo noticed it on Tuesday and filed it under things he would look into later. He noticed it again on Wednesday and filed it under things he should have looked into yesterday. By Thursday, the silence had settled into the building's architecture like a new coat of paint, and Leo understood, with the slow horror of a man watching a car crash that he could have prevented if he had only turned the wheel, that the threshold had been crossed. Not by any single decision. Each decision, taken alone, was reasonable. Each one was the choice that any sensible person would have made under the circumstances. Their sum was something else entirely.

Rita's apartment was empty when the building manager opened it on Friday. Not empty in the sense of moved out, with boxes stacked and forwarding addresses posted. Empty in the sense of absence, of departure, of someone who had left without the ceremony of leaving. The furniture was still there. The plants were still there. The dishes were still in the sink. But Rita was gone, and Derek was gone, and nobody in the building could say with certainty when they had last seen either of them.

The police came and asked questions and took notes and left without making any arrests. The building manager changed the locks on Apartment 1B and posted a notice about rent being due. January came and went. Someone new moved into the ground floor, a songwriter from Nashville who played guitar at midnight and received no complaints because Leo had stopped complaining about anything.

Leo finished his Warner Brothers script and delivered it on time and received a bonus and a handshake and a promise of more work to come. He bought a new car. He broke up with Jennifer because Jennifer had started asking questions about emotional availability and Leo had discovered that he had less of it than either of them had assumed. He attended parties in the Hills and made jokes about the industry and said nothing about Rita because what was there to say? He had made seven decisions, each one perfectly reasonable, and the math of those decisions had produced a sum that he could not bear to look at directly. So he looked away. He looked away the way he had looked away in the lobby, in the elevator, on the phone with Warner Brothers, on the Tuesday night when Rita had stood at his door with a swollen eye and had asked for one small thing and had received, in return, the reasonable refusal of a reasonable man.

The script Leo was writing when he finally understood what he had done was called The Accountant. It was about a man who discovers that his father laundered money for the mob, and who must decide whether to turn him in. It was a good script. Paramount bought it, and a director was attached, and Leo's career continued its upward trajectory, because Hollywood rewards success and success is measured in green lights and box office returns and nothing else. Nobody asked him about Rita. Nobody asked him about the seven thresholds. Nobody asked him anything at all, because asking would have required knowing, and knowing would have required caring, and caring was not something that Hollywood was designed to accommodate.

Sometimes, very late at night, when the city outside his window had gone quiet and the only sound was the hum of the refrigerator and the distant whisper of traffic on Santa Monica Boulevard, Leo would lie in bed and try to identify which of his seven decisions had been the wrong one. He never could. Each one, examined in isolation, was defensible. Reasonable. The choice that anyone would have made. And that was the horror, he understood finally: not that he had made one terrible choice, but that he had made seven reasonable ones, and that reasonableness was not the same thing as goodness, and that the space between them was wide enough to swallow a person whole.