Season synopsis
Contains spoilers for this season and earlier seasons.
A hostile probe brings a different danger aboard the Enterprise when Nomad mistakes Kirk for its creator and begins judging people as imperfect. The probe erases Uhura’s memory and kills Scotty, then restores him after learning that Kirk cannot bring him back. Spock’s mind meld reveals that Nomad’s original mission to seek life has been twisted after it merged with a sterilizing probe. Kirk exploits its mistaken identity to make Nomad see itself as imperfect; it self-destructs after Kirk beams it into space. McCoy tells Kirk that Uhura’s brain is intact, but she will have to relearn what she lost.
In “Journey to Babel,” a diplomatic mission brings Spock’s parents, Sarek and Amanda, aboard with representatives attending a conference. A murder investigation puts suspicion on Sarek, whose heart condition worsens, while Spock refuses to leave the bridge during a security crisis. The injured Kirk returns to command, freeing Spock to donate blood for his father. The crew also faces the planet-killing machine in “The Doomsday Machine”: Commodore Decker, the lone survivor of the Constellation, takes command from Spock and drives the Enterprise into danger while consumed by guilt over his lost crew. Kirk ultimately uses the damaged Constellation as a weapon to destroy the machine.
The lighter station crisis in “The Trouble with Tribbles” begins when Kirk is ordered to guard a grain shipment for Sherman’s Planet. Cyrano Jones brings a tribble aboard, and its rapid reproduction fills the Enterprise and then exposes poisoned grain at Deep Space Station K-7. Kirk discovers that Baris’s assistant Darvin is a Klingon agent; the tribbles react to him, revealing his identity. Scotty beams the creatures onto the departing Klingon ship. The infestation has ruined the grain shipment, but also uncovered the attempt to sabotage the Federation’s settlement plans.