Tomorrow, and Tomorrow, and Tomorrow Summary & ending explained

It was December in Cambridge, the kind of cold that made breathing hurt, and Sam Masur was limping off a subway car when he saw her.

She stood in the crowd on the platform, a coat too thin for the weather, dark hair pushed behind one ear. He had not seen her in years, but he knew her the way you know a song from its first two notes.

"Sadie," he called. "Sadie Green."

She did not turn. For one long second he watched her decide to pretend she hadn't heard him. Then she did turn, and her face did something complicated, and she walked over to him as if they had planned to meet there all along.

They had both grown up. She had a sharper face now, and he had a cane he pretended not to need. He was at Harvard, studying math and not loving it. She was at MIT, studying computer science and loving it too much. They traded the facts quickly, the way strangers do, and neither of them said the thing that was standing between them.

Her train came. At the last moment she pulled a floppy disk out of her bag and pressed it into his hand.

"I made a game," she said. "Tell me what you think. Honestly."

Back in his apartment, Sam's roommate, Marx Watanabe, a handsome acting student with a habit of quoting Shakespeare at breakfast, loaded the disk before Sam had his coat off. The game looked simple, almost dull. You ran a factory. You built small grey parts and loaded them onto trains as fast as you could. The better you played, the more trains left.

Then the game told you where the trains were going, and who was inside them, and what your parts were for.

Marx stared at the screen for a long time.

"Whoever made this," he said, "is either sick or a genius."

"Both," said Sam. "She's both."

Marx turned around. "You know her?"

Sam looked at the disk in his hand. He knew her. He also knew exactly why they had stopped speaking, and that it had been his fault.