StarTrek.nl - Planet

Equilibrium

While experimenting with a keyboard, the musically untrained Dax inexplicably plays a melody she seems to remember from somewhere, then suddenly develops a short temper toward her fellow crew members. She soon wanders onto the Promenade, where everyone mysteriously vanishes. A robed, masked figure stands above her, then a longer version of the melody begins to play. Dax is gripped with fear as the figure appears again, blocks her path, then removes the mask, only to reveal another. She then backs into Quark, at which point the Promenade is bustling with life again -- and the masked figure is gone.

Deep Space Nine, seizoen 3