Cadet Uhura discovers that a comet heading for a planet responds to music, while its alien guardians, the Shepherds, try to stop the Enterprise from diverting it.
Cadet Nyota Uhura, unsure whether she belongs in Starfleet, joins a dinner in Pike's quarters. The Enterprise then tries to deflect a comet headed for a planet, but the comet is protected by a force field. Uhura joins a team on its surface and discovers that the object reacts to music.
The Shepherds, aliens who escort the comet and revere it as M'hanit, an ancient arbiter of life, try to block the Enterprise. While the ship distracts them, Spock alters the comet's course, and as it passes the planet it releases water vapor that will help life flourish there. Uhura's decoding suggests the comet anticipated their interference, and Pike wonders about his own fixed fate.