At Richard and Katherine’s engagement party, the champagne had just begun to sparkle and the string quartet had found its rhythm when the lights flickered and a ripple of unease passed through the room.

That was when the Trait Swapper arrived.

No one saw a door open. No one heard an announcement. One moment the party was laughter and clinking glasses; the next, the air felt rearranged, as if the room itself had taken a breath and forgotten how to exhale.

By the time the lights steadied, Katherine stood very still near the cake table, her hand no longer resting lightly on Richard’s arm. Across the room, Richard’s best friend Byron stared at his own reflection in a silver tray, pale and shaken.

The damage-or the change-became clear in fragments.

Katherine’s posture had shifted, shoulders squared, stance grounded and confident in a way that was unfamiliar. Her voice, when she finally spoke, carried a lower register. She frowned at the music, asked what the score of the game was-any game-and launched into a precise critique of a team no one realized she had ever followed. Her tastes sharpened and hardened: competitive, analytical, restless. She moved with a physical ease she hadn’t had before, muscles responding quickly, decisively.

Byron, meanwhile, seemed lost inside himself. He blinked back sudden emotion, apologized too often, and admitted-mortified-that he felt overwhelmed by the crowd and needed a quiet corner to breathe.