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An alien lady invades the Enterprise and steals Spock's brain. Kirk, McCoy and a landing party beam down to a planet in a desperate race to retrieve it. (Season Premiere)



Kara appears on the bridge

A Sigma Draconis VI native on the bridge

The crew of the USS Enterprise follows an ion drive vessel. Scotty finds the ion engine particularly interesting. A lady from that ship transports herself onto the bridge and presses her bracelet to render everyone on the Enterprise unconscious. She slips deliberately among the crew until she finds Spock. Mysteriously, she presses her hand against the first officer's head.

Act One[]

When the crew awakens, they find that Spock is missing from the bridge. Dr. McCoy urgently calls Captain Kirk down to sickbay, where he finds Spock on a biobed. McCoy struggles to explain that, somehow, Spock's brain has been surgically removed, leaving the body alive but on full life support. Kirk proposes to find Spock's brain, but McCoy warns that the unique properties of Vulcan physiology give them only 24 hours to reintegrate it into the science officer's body.

Main viewer rear projection

The crew explores their options while searching for Spock's brain

The Enterprise uses the bulk of those hours following an ion trail to the Sigma Draconis system. Ensign Chekov places a schematic of the system on the viewscreen, pointing out that there are three class M planets. With only eight hours remaining to save Spock, Kirk has time to visit only one of the planets before Spock's body expires, so he holds an informal staff meeting on the bridge with Chekov, Sulu, and Uhura to arrive at a decision. None of them seems capable of supporting interstellar flight, but Uhura finds large, regular energy pulsations on the otherwise glaciated and pre-industrial Sigma Draconis VI. The unlikely world thus becomes Kirk's best hunch. If he is wrong, Spock will die.

Act Two[]

Kirk and Scott meet a Morg

On surface of Sigma Draconis VII, Scott and Kirk meet a Morg

Kirk, Chekov, Scotty, and two security officers beam down to the frigid surface. There, they detect five large, primitive male humanoids. Kirk's landing party prepares as the natives approach. The natives threw rocks and simple clubs at Kirk's men until Kirk phasers one who falls, stunned. The others retreat. The stunned Morg, is confused because Kirk and Scott do not seem like "the Others", whom he describes as being the givers of "pain and delight." Kirk is puzzled because the Morg does not understand what it means to have a mate nor does he seem to understand exactly what a female is.

Chekov and security guards staying warm

"It might be a long wait. We may as well be comfortable."

Chekov finds evidence of an underground city with his tricorder. Scott finds food and weapons stored in a cave, but Kirk discovers a sensor and surmises that the cave is a trap the Eymorg use to capture the male natives. McCoy beams down with Spock, whom he has fitted with a remote-controlled device to substitute for his brain. They allow themselves to be captured. Chekov and the Enterprise security officers remain above ground; Chekov uses his phaser to heat a rock to help them stay warm, since Kirk and company may be a while.

In the underground city, they encounter Luma, one of "the Others" – a race of beautiful females, the Eymorg, who live in comfort below the surface of the planet, but have the minds of children. Captain Kirk finds that he is able to establish contact with Spock's brain by using his communicator. Spock reports that he is well but that he does not know where he is. They find the woman they saw on board the Enterprise immediately before Spock's brain was removed, who renders them unconscious by pressing a button on a device located on her wrist. They are taken prisoner.

Act Three[]

Kirk, Scott, and McCoy with painbands

Kirk, McCoy, and Scott wearing Eymorg pain bands around their waists

When the landing party comes to, they find that they have been outfitted with silver belts that have large, round green devices at the abdomen. Kirk demands to know what has happened to Spock's brain, but the Eymorg do not understand what a brain is or what is the Enterprise. Finally they understand that the "Controller" the Eymorg speak of is Spock. It seems that these women have somehow connected Spock's brain into their computer and that his brain is responsible for running their expansive underground dwelling because they, as a race, have long forgotten how to take care of themselves.

Having been left alone, McCoy, Scott, and Kirk incapacitate the guards. Kirk speaks to Spock using the communicator. They inform him that his brain has been removed and it is being used as some sort of controller. Spock reports that he has a body that stretches into infinity and his medulla oblongata seems to be breathing, pumping blood, and maintaining temperature. Spock suggests that the intent to restore his brain might be impractical; he would trust McCoy to remove a splinter or lance a boil, but the knowledge to replace his brain does not exist in the universe. Kirk, however, insists that if the knowledge exists to remove his brain, there must be knowledge to put it back. He instructs Spock to send out a signal so that they may find where he is being kept. Spock complies.

Controller computer

The Eymorg Controller, home to Spock's brain

As they make their way to the chamber, Kirk asks about the belts. Spock accesses the information: one must press a red button on a bracelet in order to release the belt. They enter the chamber where Spock's brain is kept, but an Eymorg is in the chamber and activates the pain belt. Kirk uses the remote control device to use Spock's body to grab Kara's bracelet and press the red button, releasing the belts. With the crew freed, Kara pleads that Spock's brain must remain connected or their civilization will die.

Kirk tells Spock that he is in a black box connected by light rays to a control panel. He wonders if the sensations he is feeling means that Spock is recirculating air, running heating plants, and purifying water. Kirk asks Kara how she was able to remove Spock's brain by placing on her head a device known as the "teacher". They place it over her head, and she suddenly speaks with erudition. She admits that she does have the knowledge, but she also now knows to use a phaser, which she points at Kirk. It is set to kill.

Act Four[]

Kara aims phaser at James T

"That phaser is set to kill."

Kara and Kirk debate over the proper disposition of Spock's brain. Scott pretends to faint and distracts Kara; they obtain the phaser from her. She says that the teacher will provide knowledge for three hours, which McCoy says would be just long enough to effect the transplant, but she refuses to perform the operation. McCoy points out that he has medical knowledge and should be able to use what he already knows and retain the knowledge. McCoy places the teacher on his head and receives the knowledge; when he recovers, he says "Of course; of course. A child could do it. A child could do it."

McCoy using the Great Teacher

McCoy endures the pain of the Teacher's "lessons"

McCoy begins quickly restoring Spock's brain, using the same knowledge originally used to remove it. However, after a time, McCoy begins losing the knowledge he has gained. He exclaims in despair, "I am trying to thread a needle with a sledgehammer!" Drawing on his own skills with only a few minutes left, he connects Spock's speech center, allowing Spock to speak. Spock then assists McCoy in completing the reconnection of his brain. "I'll never live this down," McCoy says, "this Vulcan is telling me how to operate."

Upon his restoration, Spock makes a speech that explains the history of this retrograde civilization and the split of the sexes. McCoy then laments, "I should have never reconnected his mouth." "Well, we took the risk, doctor," Kirk jokes.

Log entries[]

Memorable quotes[]

Spock brainless

"His brain is gone!"

"His brain is gone!"

- McCoy to Kirk, as Spock lies unconscious in sickbay

"What if you guess wrong, captain?"
"If I guess wrong, Mr. Spock is dead. Spock will die."

- Chekov, when Kirk selects Sigma Draconis VI as the possible location of Spock's brain

"Call Chekov and tell him to send my stomach down."

- McCoy, after rapidly descending in the Sigma Draconis VI elevator

"Brain and brain! What is brain?!"

- Kara, frustrated by the constant inquiries about Spock's brain

"Pain and delight, he said up above."
"I'm sure you noticed the delight aspect."
"Yes, I certainly did notice those delightful aspects."

- Kirk and McCoy, on the females of Sigma Draconis VI

"This fellow is keeping us from our property."
"Well, isn't there a way to correct that situation?"

- Kirk and Scott, before overpowering the guards

"While I might trust the doctor to remove a splinter or lance a boil, I do not believe he has the knowledge to restore a brain."

- Spock, on McCoy's difficulty in restoring his brain

"The Controller is young and powerful. Perfect!"
"How very flattering."

- Kara and Spock, after the pain bands fly off from Kirk, McCoy, and Scott

"No one may kill a man. Not for any purpose. It cannot be condoned."

- Kirk to Kara, as she points a phaser at him

"A child could do it."

- McCoy, after receiving the medical knowledge from the Great Teacher

"I should have never reconnected his mouth."
"Well, we took the risk, doctor."

- McCoy and Kirk, after Spock starts describing the culture of Sigma Draconis VI

Background information[]

Production timeline[]

Story and script[]

  • This was the third season's premiere, written by "Lee Cronin", the pseudonym of former writer and producer Gene L. Coon. Based on his April 1968 story outline, this episode underwent significant revisions before the final draft. [1] Among the early concepts:
    • Spock's brain was taken while he, Kirk, and McCoy were exploring the surface of an asteroid.
    • The antagonists were from the planet "Nefel," and were known as the "Nefelese." Their leader is a male named "Ehr Von." Also, there is no mention of the "Teacher."
    • When Kirk contacts Spock's brain, he instructs the brain to go into the slon porra, the Vulcan state of complete mental control.
    • McCoy received no transfusion of any special surgical knowledge except for a study of the planet's advanced surgical techniques. Only when combined with his existing surgical knowledge is he then able to perform the surgery.
    • After McCoy completes the brain implant surgery, Spock experiences several side effects from McCoy having reversed the connections of several nerve endings, causing Spock to, among other things, laugh when he wants to sneeze. He is, however, able to restore the errors with his own mental disciplines.
  • Co-Producer Robert H. Justman, who described the episode as being "late lamented," contributed to this story by suggesting that Spock's brain direct Doctor McCoy in the operative procedures of replacing it into Spock's body. (TOS-R Season 3 DVD special features)
  • In Up Till Now, his 2008 autobiography, William Shatner jokes that the plot of this episode is a "tribute" to NBC executives who had slashed the show's budget and placed the show in an undesirable time-slot.
  • This is the only episode title of the original series that includes an Enterprise crew member's name. Characters that received a title mention in later series include Q with eight titles, Data with three, Julian Bashir with two, one for each of Deanna Troi, Ro Laren, Aquiel Uhnari, Melora Pazlar, Jadzia Dax, Quark, Morn, Lore, and Rajiin.


  • This was the last episode to be directed by regular Trek director Marc Daniels. Daniels was unhappy with the budget cuts the series suffered for the third season and the direction it was taking overall, and declined to come back to helm more episodes. (These Are the Voyages: TOS Season Three) However, Daniels later wrote the episode "One of Our Planets Is Missing" for Star Trek: The Animated Series and directed the pilot Planet Earth for Gene Roddenberry.
  • The score for this episode (by Fred Steiner and recorded on 26 August 1968) was re-used in later episodes during the playback of Kirk's final message in "The Tholian Web" and Kirk's return in the transporter room in the same episode, for example. The battle music from this episode later scored Kirk and Kang's sword fight in "Day of the Dove".
  • This is the first and only episode besides the first pilot where characters walk in front of the main viewscreen showing a moving starfield. This was achieved by using rear projection instead of the usual post-production matte used in viewscreen shots.
  • A gag scene was filmed during the production of this episode, showing Leonard Nimoy in handcuffs, with a prop gun pointed at him, holding a newspaper with the headline, "Spock gets two-year prison term". Psychologist Benjamin Spock was sentenced to prison after encouraging draft evaders and claiming the Vietnam War to be anti-constitutional on 11 July 1968, during the filming of this episode. [2]
  • During one of the takes where Kara reaches for Spock's head, Leonard Nimoy reaches up and grabs "Kara"'s wrist, ostensibly to prevent her from stealing his brain. (Star Trek: Lost Scenes)


Sets and props[]

Spock wearing neural stimulator

Spock's control device


  • The jumpsuit that Leonard Nimoy wears on the planet's surface appears to have been the same one he wore in "This Side of Paradise", complete with black shirt.


  • This is the only instance of Sulu recording a log entry while in command during TOS. In his log entry, he refers to Sigma Draconis VI as Sigma Draconis VII, a mistake Kirk made in an earlier log entry as well. The lexicon in the Star Trek Concordance also makes note of this oversight in dialogue. Kirk also lists the wrong "stardate" at the beginning of Act Two as 4351.5, when it is supposed to be 5431.5.
  • This marks the third of five times that Sulu is seen in the captain's chair while temporarily in command. The first time happened in "Errand of Mercy", the second in "The Enterprise Incident". The last two occur in "The Lights of Zetar" and "The Savage Curtain".
  • Like their Human counterparts ("male" and "female"), Morgs (all male) and Eymorgs (all female) have similar names to each other.


  • The novelization of this episode explained that McCoy was the only person who could use the Great Teacher since he had pre-existing medical knowledge, showing why the other members of the crew could not use the Great Teacher to assist in healing Spock.

Remastered information[]

The remastered version of "Spock's Brain" aired in many North American markets during the weekend of 9 June 2007.

The episode marked several script-appropriate departures from the original broadcast version. Given the generic design of the original ion starship, it would seem unlikely that Scotty could have recognized its propulsion system just by the hull design. The remastered version thus gives the hull a unique, easily identifiable shape.

The CBS description of the model stated:

"In the episode "Spock's Brain" the ion propulsion spacecraft spotted by the Enterprise in 2268 certainly impressed Scotty with its design and technology. The comparison between the original and the remastered version provides two totally different looks, with styles defined more by the contemporary technology. The original is a standard rocket-shaped configuration. At the time, "spaceships" tended to fall into one of two classic looks, the other being the flying saucer.The new, remastered version of the ion propulsion craft is smaller and more utilitarian, reflecting its single-person occupancy, and it ditches the unnecessary missile/rocket configuration. The design also reflects more modern-day ion propulsion prototypes."

The planet Sigma Draconis VI received a fresh, computer-generated appearance both from orbit and from the surface. In the original orbit shot, the planet appears to have a wide band of ocean peeking out from a less-than-uniform ice cap. In the remastered version, the ice coverage is solid, with only small strips of land present, as the script demands, "at the tropics". Also, the color of the planet from orbit closely matches the color of the land on the surface. On the surface, the landscape has been modified as well. In the original, there was only a slight indication that the action was taking place on a planet that was mostly ice. By contrast, the remastered version makes this more apparent through the use of a new matte painting. [3]

Video and DVD releases[]

Links and references[]


Also starring[]


Guest star[]


Uncredited co-stars[]

Stunt doubles[]


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External links[]

Previous episode produced:
"And the Children Shall Lead"
Star Trek: The Original Series
Season 3
Next episode produced:
"Is There in Truth No Beauty?"
Previous episode aired:
"Assignment: Earth"
Next episode aired:
"The Enterprise Incident"
Previous remastered episode aired:
"Bread and Circuses"
TOS Remastered Next remastered episode aired:
"Plato's Stepchildren"