“I’ll only jog when everyone else does,” she told them. And indeed, in the summer months when she went out at seven in the morning, there were dozens of people doing the same thing. “Jackie Onassis jogs round the reservoir, too,” she told her mother. Not that she’d ever seen Jackie Onassis, but she’d heard it was true, and she hoped it would help to reassure her.

This summer, there was another threat to worry them.

“I just wish the police would catch this terrible man,” her mother would say, whenever she telephoned. Maggie couldn’t blame her. The Son of Sam, as he called himself, had scared a lot of people in recent months, shooting young women, and sending strange letters to the police and a journalist, stating that he would strike again. His attacks had been in Queens and the Bronx so far, but reminding her mother of this fact had done no good. “How do you know he won’t strike in Manhattan next?” she had said, and of course Maggie hadn’t got an answer.

It had been stiflingly hot and close all day. It felt like the start of a serious heatwave. She had changed into a light cotton skirt and blouse, and she was looking forward to a long, cold drink.

Juan Campos stood on the sidewalk and stared across the great divide. He too had noticed the hot and muggy weather, and right now, he sensed a heavy, electric feel in the air. He expected the rumble of thunder at any time.

He looked toward Central Park. His girlfriend Janet lived on the West Side, on Eighty-sixth near Amsterdam. She was walking across the park to meet him.

An ambulance, siren moaning and horn blaring, came round the corner from Third Avenue and raced along the north side of the street toward Madison. This was nothing out of the ordinary. There were always ambulances making a noise on East Ninety-sixth Street, because the hospital was so nearby.

Juan was standing at the intersection of Ninety-sixth and Park. The apartment he’d recently moved into was the other side of Lexington Avenue, on the north side. He had a sublet for a year, and he had no idea whether he’d be there for longer. Nothing in his life so far had ever been certain, so he didn’t suppose it would be now. But at least one thing was consistent: he was still living on the north side of the great divide.

His street. Ninety-sixth Street. It was a cross street of course, like Eighty-sixth, and Seventy-second, Fifty-seventh, Forty-second, Thirty-fourth and Twenty-third. The traffic moved both ways. If each of these great streets had their particular characters, Ninety-sixth Street, in the year 1977, was something entirely different. It was the border between two worlds. Below Ninety-sixth Street lay the Upper East and Upper West sides. Above it was Harlem, where people like his friend Gorham Master didn’t go. But if most people from outside the city assumed that Harlem was nowadays all black, they would have been quite wrong. There were numerous other communities in Harlem, but the largest of these, by far, lay in the southern portion, above Ninety-sixth and east of Fifth.