The title was unassuming, but the thread below it was a graveyard of "File Deleted" messages and warnings. One user had simply written: It’s not music. It’s a floor plan.

The recording ended with a final, whispered instruction: “Don’t look for Part 2.”

He sat frozen in the blue light of the monitor. From the darkness of his own apartment hallway, he heard the exact same click he’d heard at the beginning of the file.