"Space Seed" is a first-season episode of Star Trek: The Original Series, that was first broadcast on February 16, 1967 and repeated on August 24, 1967. It is episode #22, written by Gene L. Coon and Carey Wilber, based on a story by Carey Wilber, and directed by Marc Daniels.
On stardate 3141.9, the starship USS Enterprise, under the command of Captain James T. Kirk, finds a derelict ship floating in space. The ship is identified in historical records as the SS Botany Bay, a DY100 class freighter, that was modified as a sleeper ship for cryogenically frozen passengers. It was launched from Earth sometime during the 1990s, in an era known as the Eugenics Wars.
Scanning for signs of life, Dr. Leonard McCoy confirms that there is something still alive on board, but is not quite sure if it is human. A landing party consisting of Captain Kirk, Dr. McCoy, Mr. Scott and crew member Lt. Marla McGivers, is formed and beamed over to the freighter. McGivers is brought along because she is a historian who specializes in late 20th Century history and culture.
As expected, the landing party finds the cargo of 84 humans, 73 of whom are still alive, remaining in suspended animation. Despite being nearly 300 years old, they have not aged a day. McGivers finds the stasis tube that contains the body of who she believes may be the group's leader. Suddenly, the machinery of the capsule lights up and the male occupant inside appears to be reviving. McCoy realizes the life support system is failing and the occupant may die. Kirk breaks the glass door and pulls the man out to revive him. The man is taken back to the Enterprise for a medical examination.
Kirk has the Botany Bay taken in tow by a tractor beam and sets course to Starbase 12 in the Gamma 400 Star System. Meanwhile in sickbay, Lt. Givers marvels over the man who is a living relic from an era she has studied all her life. McCoy believes he will recover shortly and should be well enough to answer questions. McGivers leaves sickbay, and suddenly McCoy finds a sharp scalpel at his throat courtesy of the patient. The man is awake, and demands to know where he is. McCoy responds by suggesting that if the man is going to kill him, he should do so by cutting the carotid artery quickly and cleanly. Impressed with McCoy's bravery, the man puts the scalpel down and introduces himself as Khan.
Mr. Spock discovers that Khan Noonien Singh and his people were products of the Eugenics Wars, where genetic supermen were bred as perfect soldiers. The soldiers instead became warlords and dominated over 40 countries in and around Asia. Toward the end of the Eugenics Wars between 80 and 90 of them were unaccounted for. Khan is recorded as being the most dangerous of these warriors and alone he dominated a quarter of the Earth.
In the meantime, Khan is given spacious quarters, however he protests the armed guard and locked door. Lt. McGivers is sent to talk to him and debrief him on current events. It is clear that McGivers is falling in love with the handsome and powerful leader. Khan takes advantage of her overt kindness and tells her that he plans to rule mankind once again and needs her help to take over the Enterprise. At first McGivers refuses to help, but soon she falls more deeply for Khan's charms. Reluctantly, she tells Khan she will do whatever he asks.
Khan and McGivers secretly beam over to the Botany Bay and revive the remaining survivors of Khan's people. They return to the Enterprise in force and seize control. Khan cuts off life support to the bridge and the command crew passes out. Khan later throws Kirk into a decompression tank and slowly suffocates him until Kirk's command crew promise to follow him. Feeling guilty for betraying her ship, Lt. McGivers relents and frees Kirk from the chamber. Kirk then helps Spock escape his captors and the two inject a nerve gas throughout the entire ship to disable Khan and his hijackers.
Khan manages to escape the gas and heads down to engineering where he attempts to destroy the Enterprise, but Kirk runs in and a brawl ensues. It looks at first that Kirk is overmatched, but he manages to pull a tool from a console, and using it as a weapon, knocks Khan out.
When Khan and the hijackers are rounded up, Kirk holds a hearing to decide their fate. Kirk decides that Khan and his followers should be exiled and picks Ceti Alpha V, a lush but treacherous world that Kirk believes would be perfect place for Khan to start his kingdom over again. Life on Ceti Alpha V will not be easy, but Khan, impressed with the idea, claims he is up to the challenge and accepts Kirk's offer. Instead of a lengthy court martial for Lt. McGivers, Kirk allows her to go into exile with Khan.
Spock makes a statement at the end, saying that he'd like to see what Khan makes of Ceti Alpha V in 100 years. This story is continued in the motion picture film Star Trek II: The Wrath of Khan.
The episode marks the first mention of the Starfleet rank of Fleet Admiral. The rank is discussed in passing when Leonard McCoy, observing a dinner set for Khan, remarks that the ship must be expecting a Fleet Admiral for dinner. An actual Starfleet Fleet Admiral, however, is not seen on camera until Star Trek III: The Search for Spock.
The nature of Khan's genetically enhanced followers would be explored further in a three-part episode arc on Star Trek: Enterprise in 2004. Taking place a century prior to the events of "Space Seed", the episodes ("Borderland", "Cold Station 12" and "The Augments") featured a group of people from the same genetic experiment that produced Khan and his people. These people come to be referred to as Augments, although this term is not used in this episode to describe Khan and his men. The human augments in Star Trek: Enterprise seem to be aware of The Botany Bay, but their human leader (and criminal) Arik Soong assures them that its a myth. This is a retcon joke because althought Enterprise is set earlier in history than Space Seed it was produced later.