On August 28th, 2199, at approximately 11:40, a woman in the open-air section of Shelf Market Seven began to dance. Not rhythmically. Not recreationally. Her body moved in continuous, repetitive, involuntary motion — limbs cycling through a pattern that resembled no known dance form but was unmistakably choreographed. She was screaming. She could not stop.

Within thirty minutes, forty-one additional people in Market Seven had begun the same motion. Not similar — the same. Identical patterns, identical tempo, as if broadcast to their motor cortices from a single source. BCI scans on the affected showed no external signal intrusion. No malware. No hijacked neural pathways. Their bodies were simply doing something their brains had not asked them to do, and their brains were fully aware, fully conscious, fully horrified.

The event lasted nineteen hours. By hour six, the first victims began to collapse from exhaustion, dehydration, and cardiac stress. Medical teams could not physically restrain the affected — their muscles operated with a strength that exceeded their normal capacity, as if whatever drove the movement had overridden the body's safety limiters. Sedation was partially effective. Full paralytic agents stopped the movement but induced immediate respiratory arrest in three cases. Forty-seven people were affected in total. Forty-seven people danced. Forty-seven people could not stop. Twenty-three were hospitalized. Four died.

The vector was never identified. Epidemiological mapping shows no commonality among victims — different ages, different districts, different BCI manufacturers, different neurotypes. The only shared factor was physical presence in Market Seven during the initial thirty-minute window. Air samples, surface swabs, and electromagnetic surveys of the area revealed nothing anomalous. Market Seven reopened three days later. No one dances there anymore. No one plays music there anymore either.