Every evening, Mira sat on the underpass steps and played the same eleven notes. She never named the tune. It just showed up in her fingers one cold winter and stayed. Coins dropped into her open case while she played. But tonight a padded envelope was already waiting on the step. The address was written in her own slanted handwriting, even though she had never mailed a thing in her life.

Mira flipped the envelope over. No stamp, no return address, just a tiny printed symbol in the corner: a circle with eleven dots around it. It was the same shape she sometimes doodled without thinking. A van with that exact symbol on its door sat parked at the top of the stairs.

Mira climbed the stairs to the van. The door slid open before she even touched it. Inside sat a single chair, a screen, and a keyboard with exactly eleven keys. On the screen, a message blinked: 'Welcome back, composer. Ready to finish the song?'

Mira sat down and pressed the eleven keys in the backward order from the envelope. The screen filled with light, then showed a face: her own, but calm and certain. 'You built this machine to send the song to your younger self,' the face said. 'You're almost done. Press play.' Mira's finger hovered over the last key.