At the party, he saw her ghost before he saw her.
They were nearly the same height. The woman was laughing at something, turned toward the window, and the ghost stood half a step behind her and to the left, not laughing, watching the room with the attention of someone who had learned to watch rooms carefully.
He had never been able to explain what made the ghosts visible to him. They were simply there, occupying space that was also occupied by someone else, present in a way that required no explanation from the world. As a child he had assumed everyone could see them. He had learned, slowly, that he was wrong.
He had also learned not to pay them too much attention. The ghost was never the person you were talking to. The ghost could not order a drink or remember your name. The ghost was information about a person, not the person.
He reminded himself of this while crossing the room.
She was interesting. Precise in the way she chose words, attentive in a way that felt earned rather than performed. He liked her. He was also aware, in a way he could not switch off, that the ghost was more interesting.
The ghost's eyes held something the woman's eyes did not. He had looked at a hundred unlived selves over the years and never quite found a word for the quality. Watching this one, the closest he could get was: I know what question you are not asking.
He wanted to ask it. He got her number instead.
They went on three dates. She was guarded and occasionally funny in a way that surprised him. The ghost was always present, always watching. On the fourth date he said, without planning to: "Who were you going to be?"
She went still.
"I don't know what you mean," she said.
He could have said never mind. He could have changed the subject. The ghost was watching him from beside the window.
"I think you do," he said.
The silence was long enough for several things to happen inside it. He watched her decide something.
"A mathematician," she said. "I was going to be a mathematician. My mother was sick. I came home. And then there was no going back."
She looked at her wine. He looked past her at the ghost, whose expression had shifted into something he recognized from other faces, other unlived selves: the particular quality of being seen by someone who was not supposed to be able to.
"I can see her," he said. He had never said this to anyone.
She looked at him for a long moment. Then she turned, very slowly, toward the space just behind her left shoulder, where she seemed to have always half-known something was standing.
"What does she look like?" she said.