Spock/Starfleet/James T. Kirk/Year Four

At some point around Spock's fourth year on the Enterprise, he was offered an assignment with Medusan Ambassador Kollos which he turned down, as he claimed that he "was unable to accept," as his "life is here," aboard the Enterprise. The assignment, instead, went to Miranda Jones. ()
In 2268, Spock and other crewmembers of the Enterprise encountered Harry Mudd stranded on a planet of androids. The androids wanted the Enterprise to escape the planet and serve Humans so that they would not have to explore space. Kirk, Spock, and the rest of the crew eventually managed to overload the androids' central control by acting in a illogical manner, causing the chief android, Norman, to have a breakdown. ()
While traveling to a peace conference on Babel, Spock was reunited with his parents. There was still much friction between Spock and his father. When Sarek was accused of the murder of another delegate, it was revealed that he was ill with a cardiac defect which made it unlikely that he could have committed the crime. McCoy was then tasked with performing surgery on Sarek while in a space battle with an enemy ship. It was then discovered that Orions were responsible for the murder, and Spock made himself available for a blood transfusion for his father's surgery because they shared the same rare blood type, T-negative. Recovering in sickbay, Sarek and Spock made peace with each other, even playfully teasing Amanda. ()
On stardate 4523.3, Spock helped foil a Klingon plot to poison quadrotriticale earmarked for Sherman's Planet while at the same time trying to clear the Enterprise of a fast-breeding alien species called tribbles. (; )
Spock later visited Sigma Iotia II whose inhabitants had modeled their society on the gangster era of Earth's 1930s. An earlier starship had left behind a book about gangsters from Earth's 20th century that the imitative Iotians had used as a blueprint for their society. Spock played the part of one of the bosses of the main syndicate, "The Federation," and helped Kirk unite the two warring bosses into a form of government. ()
Spock, along with the Enterprise, encountered a space amoeba that destroyed entire star systems. The , which was sent to investigate the phenomenon, was destroyed, and Spock felt the Vulcans on the ship dying. In order to gain information on the creature, Spock piloted a shuttle into the amoeba and found that it was about to reproduce by fission. He subsequently destroyed the creature with an antimatter bomb. ()
Spock's body was later taken over by Henoch, one of three survivors of an ancient civilization that had destroyed itself. The three had become energy beings to survive and wished to build androids to house their minds. Henoch, the rival of fellow survivor Sargon, refused to relinquish Spock's body and attempted to kill Sargon. He himself was killed with the help of Spock's consciousness and Sargon's wife Thalassa. ()
Spock came in contact with various other worlds in the early part of 2268. He was captured by Ekosians who had based their society on that of Nazi Germany and tortured him for information about the Enterprise. John Gill, a Federation historian, had visited Ekos and attempted to use the efficiency of Nazi Germany to bring stability to the planet. Toward the end of the encounter, it was found out that Gill was drugged by his deputy Melakon. Through the use of the mind meld, Spock helped bring Gill to almost full wakefulness. ()
Spock battled Kelvans who tried to take over the Enterprise in order to return to their homeworld in the Andromeda Galaxy. He helped Kirk stop Ronald Tracey, a Federation captain interfering in Omega IV's societies by arming the Kohms against the Yangs. He battled the government of a planet where a Rome-like civilization had never fallen and gladiatorial games still took place in the planet's modern era. ()
Later the same year, Spock's brain was stolen by the Eymorgs to help power the Great Teacher that controlled their society and provided for all their needs. McCoy was able to reconnect Spock's brain to his body with the same technology used to remove it. ()
Spock, along with Kirk, stole a cloaking device from the Romulans. As part of the plan to retrieve the device, he pretended to kill Kirk in self-defense and romanced the craft's commander in order to gain her trust. He initially intended only to carry out his mission but experienced actual feelings for the beautiful and brilliant commander. After Kirk returned to the Romulans' craft disguised as a Romulan and stole the device, Spock stalled the Romulans long enough for the device to be installed in the Enterprise. The ship escaped with the cloaking device and the Romulan commander on board, who made a pact with Spock to keep their mutual feelings for the other a secret. ()
Spock later saved Kirk and a tribe of transplanted Native Americans when he helped save their planet Amerind from an asteroid by activating a deflector beam. () He allowed Kollos to take over his body so that he could guide the Enterprise back into the galaxy after a mad Larry Marvick had driven it into an uncharted region. The Medeusans were a highly intelligent species but their bodies were grotesque in form – so much so that gazing upon a Medeusan would cause instant insanity in humanoids. However, it was said that telepathically viewing a Medeusan's mind, as Spock did, was quite a beautiful experience. ()
Spock helped save an landing party from the Melkotians who had, as punishment for trespassing, forced them to relive the infamous gunfight at the OK Corral in a recreation of Tombstone, Arizona. () He also helped redirect Yonada from colliding with Daran V. ()
Spock took command of the Enterprise when a spatial interphase trapped Kirk between universes. Despite a Tholian attack from Commander Loskene, Spock and the Enterprise crew managed to retrieve Kirk and escaped from the Tholians' energy web. ()
A race of psychokinetics later captured Spock, Kirk, and McCoy. The aliens forced them to take part in dangerous games and unwanted love affairs. ()
After hyper-accelerated aliens took over the Enterprise and hyper-accelerated Kirk to take as a hostage, Spock managed to receive a warning from Kirk and became hyper-accelerated himself but carried an antidote with him. He and Kirk stopped the aliens and retook the ship. ()
Spock was part of a landing party that aliens were using to test the worthiness of an empathic race. A supernova was going to destroy their planetary system, and the aliens wanted to see if their race should be saved. After the aliens tortured Kirk, Spock, and McCoy, the empath healed them. Impressed by this, the aliens saved her planet. ()