(written from a Production point of view)
Kirk and Spock try to protect the planet Organia from the Klingons, but the natives don't want the Federation's help.
Coded orders from Starfleet Command to the USS Enterprise disclose that negotiations with the Klingon Empire are on the verge of collapse and that Starfleet expects a surprise attack. The Enterprise is ordered to Organia, a peaceful, Class M planet in the disputed area, to prevent the Klingons from using it as a base of operations.
En route, a Klingon vessel suddenly attacks the Enterprise with magnetic pulses. Kirk orders the phaser banks to lock on and return fire. After a brief weapons exchange, the Enterprise destroys the Klingon ship with a proximity blast set at a 100% dispersal pattern. Lieutenant Uhura receives a Code One alert from Starfleet: War with the Klingons has begun and Captain Kirk resolves to reach Organia "before the hammer falls", as the trigger has now been pulled.
Assuming orbit, Kirk and Spock beam down to the planet, leaving Lieutenant Sulu in charge, with specific duties "to the Enterprise, not to us" and, if outnumbered, to avoid combat and immediately warn Starfleet.
Upon beaming down to the surface of Organia, Kirk and Spock find a primitive, agrarian society whose people seem curiously unconcerned about visitors materializing within their midst — which makes Kirk wonder whether the Organians "get people beaming down every day". Ayelborne welcomes them, but tells Kirk "we don't have anyone in authority." But, as Chairman of the Council of Elders, he invites them to the Council chambers.
However, the councilors tell Kirk they have no need of protection nor defenses; they do not believe the Klingon invasion poses any threat to their people or their culture or way of life. While they recess to discuss Kirk's offer, Spock discloses that the culture has not advanced for as far back as his tricorder can measure; Organia is "an arrested culture."
The Council's discussions result in no change, and they can see no benefit to affiliation with the Federation. Then the Klingon fleet of D7-class battle cruisers arrives – a fact Councilor Trefayne somehow seems aware of before even Spock can confirm it with his tricorder, surprising him and Kirk.
The Enterprise is forced to leave, stranding Kirk and Spock amid a Klingon occupation army, led by Kor.
The Organians provide Kirk and Spock with native clothing, but take their weapons. Kirk is now Baroner, a leading Organian citizen, while Spock is a Vulcan merchant dealing in kevas and trillium. But Kor considers Spock a spy, since Vulcans are members of the Federation, and takes him in for questioning. When Kirk protests, Kor decides that Kirk is "a man I can deal with" as his liaison to the civil population.
The examination, performed with the mind scanner, does not pierce Spock's pretense, and he is released. Kirk has been instructed in his duties as liaison, and both men are released to go about their business. Formulating a plan to fight against the Klingons, Kirk and Spock destroy a Klingon ammo dump – and find that the Organians are appalled by the mere thought of violence. Kirk tells Ayelborne that the Organians can resist a military dictatorship, but Ayelborne replies that Kirk simply doesn't understand them. Unfortunately, Kor has the Council chamber under surveillance and hears everything.
Ayelborne, learning Kor's plan to interrogate Kirk with the mind sifter, reveals Kirk's identity. Betrayed, Kirk and Spock are taken prisoner and threatened. But Ayelborne remains placid, assuring Kirk that no harm will come of it. Kirk and Kor discuss their differing ideologies; Kor is pleased that the universe is full of people who don't like the Klingons. Kirk is given twelve hours to answer questions about Starfleet's starship deployments; otherwise, he will be subjected to the mind sifter, becoming a vegetable, and Spock will be dissected to determine how he can resist it. Kirk tells Kor he will need a lot more than twelve hours to get the necessary information out of him. Kor tells Kirk that he will get the necessary information from him at the designated time as war is a game that the Klingons intend to win.
With just over six hours left, the cell door opens, but it is Ayelborne, offering them safe passage back to the Council chambers, where he assures them the Klingons will not come. Kirk cannot understand how their betrayer is now their rescuer. He does not initially trust Ayelborne, but as the Organian informs him he has very little choice. When asked where the two Klingon guards are, Ayelborne simply states nothing happened to them.
When informed of the escape by his lieutenant, Kor is furious. The Klingon officer reports that the two Klingon guards were simply not there with no other exit. Kor gives a Special Occupation Order 4. Kirk, Spock and the Organians hear disruptor fire and, on the loudspeakers, that hostages will be killed: two hundred immediately, and two hundred more at two hour intervals until the "Federation spies" are returned.
Kirk plans a suicide assault on Kor's stronghold that evening to save Organian lives. The council returns the officers' phasers, then confer privately that, "Of course, we cannot allow it."
Darkness falls, and Kirk and Spock begin their assault, resolving to stun and not kill, as "we're after the top dog." They disable Kor's lieutenant and gain entry to Kor's office. Kirk doesn't plan to kill Kor; Kor wants to discuss the prospects for war, on the surface and in space. For example, even Kor's office is under surveillance.
But, as Klingon troops stream in, everyone's weapons become too hot to handle — and the same is true on every ship in both warring fleets. Ayelborne and Claymare enter Kor's office, apologize for being forced to intervene, but announce that they have put a stop to the violence.
Ayelborne states that, as he stands before Kirk and Kor, he also stands on their respective homeworlds, Earth and Qo'noS. Both sides must agree to cease hostilities, or their armed forces will be immobilized. While insisting that nobody wants war, Kirk seems equally annoyed at its interruption as is Kor. He states they have legitimate grievances and that they have a right to handle it as they see fit. Ayelborne tells them that in the future, their races will eventually become fast friends and will work together, which Kor finds unbelievable. Claymare says the visitors' discordant emotions require that they must leave. Ayelborne discloses that none of the two hundred Organian hostages have been killed, and what Kirk and Kor see is merely for appearance. The Organians have over millions of years evolved beyond the need for physical bodies, and have become advanced and powerful energy beings. Kirk and Spock work out themselves that Organia's outward appearance was solely to provide points of reference for visitors. Ayelborne and Claymare disappear before Kirk, Spock and Kor's eyes, changing from human form into very bright pure energy. Kirk turns to Kor and tells him it looks like they will not be going to war after all. "A shame, Captain. It would have been glorious", the Klingon commander states.
Back on board the Enterprise, Kirk admits to Spock at being embarrassed that he was furious with the Organians from preventing a war with the Klingons – a war he did not want. Kirk tells Spock that they often think of themselves as the most powerful force in the universe, it's unsettling to find out they ultimately are not. Spock tells Kirk that he and himself have no reason to be embarrassed; it took millions of years for the Organians to evolve into what they are now. Spock points out that even the gods did not come into being overnight. Spock also says that at least they beat the odds in not dying on the planet. Kirk tells Spock he is wrong, as they didn't have a chance at beating the odds. "The Organians raided the game."
"War. We didn't want it, but we've got it."
"Curious how often you Humans manage to obtain that which you do not want."
- - Kirk and Spock, as the Federation-Klingon War starts
"I'm a soldier, not a diplomat. I can only tell you the truth."
- - Kirk, to the Organian Council of Elders
"This is the ruling council?"
"I am Ayelborne, temporary head of the council. I bid you welcome."
"No doubt you do. I am Kor, military governor of Organia."
- - Kor and Ayelborne
"Have we a ram among the sheep?"
- - Kor, to "Baroner"
"I don't trust men who smile too much."
- - Kor, on the Organians
"You don't have to be sheep. You can be wolves."
- - Kirk, to Ayelborne
"Always it is the brave ones who die. The soldiers."
- - Kor, taking Kirk and Spock as his prisoners
"What would you say the odds on our getting out of here?"
"Difficult to be precise, Captain. I should say approximately 7,824.7 to one."
"Difficult to be precise?"
- - Kirk and Spock, before attacking two Klingon guards
"Attention. Attention, all Organians. Attention. This is Commander Kor. The two Federation prisoners have escaped, obviously with outside aid. They will be returned immediately. So that you will know we mean what we say… listen."
"Those are Klingon phasers. Take the door. Get down, gentlemen."
"In the courtyard of my headquarters, two hundred Organians have just been killed."
"Two hundred of them…"
"In two hours, two hundred more will die, and two hundred more after that until the two Federation spies are turned over to us. This is the order of Kor, son of Rynar."
- - Kor and James T. Kirk
"Today we conquer! Oh, if someday we are defeated… well… war has its fortunes. Good and bad."
- - Kor
"We have the right –"
"To wage war, Captain? To kill millions of innocent people? To destroy life on a planetary scale? Is that what you're defending?"
- - Kirk and Ayelborne
"It is true that in the future, you and the Klingons will become fast friends. You will work together."
- - Ayelborne, to Kirk
"I should say the Organians are as far above us on the evolutionary scale as we are above the amoeba."
- - Spock, after the Organians reveal their true forms
"Well, Commander, I guess that takes care of the war. Obviously the Organians aren't going to let us fight."
"A shame, Captain. It would have been glorious."
- - Kirk and Kor
"Even the gods did not spring into being overnight."
- - Spock, to Kirk
"You and I have nothing to be embarrassed of. We did, after all, beat the odds."
"Oh no, Mr. Spock, we didn't beat the odds, we didn't have a chance. The Organians raided the game."
- - Spock and Kirk
Story and script
- This episode marks the first appearance of the Klingons. Story editor Dorothy Fontana thought the Klingons were made the regular adversaries of the series because they didn't need any special (and expensive) make-up like the Romulans, whom she thought to be much more interesting. 
- Ayelborne mentions that in the future, the Federation and the Klingons would be friends and work together, both of which become true.
- The episode title comes from The Life and Adventures of Nicholas Nickleby by Charles Dickens: "It is an errand of mercy which brings me here. Pray, let me discharge it."
- In the script, the Klingons were described simply as "Oriental, hard-faced." 
- According to the script, the Organian village was to be modeled on old English villages, with thatched huts and muddy back alleys.
- This is the first episode in which Sulu is shown sitting in the command chair, although he had previously commanded the bridge from the helm position in "Arena". Scott, who doesn't appear in this episode, had commanded the Enterprise in the absence of Kirk and Spock in "A Taste of Armageddon", in which Sulu didn't appear. The second season would establish Scott as senior to Sulu in the command structure.
- DeForest Kelley (McCoy) and James Doohan (Scott) do not appear in this episode. Along with "What Are Little Girls Made Of?" and "The Menagerie, Part II", this is one of only three episodes after the two pilots in which Kelley does not appear. This was also McCoy's last non-appearance in TOS. It was not until season two that the two encountered Klingons.
- This was the first appearance of John Colicos as Kor. The character was also set to appear in "Day of the Dove" and "The Trouble with Tribbles", but Colicos was unavailable and other Klingon characters were written in. A script was written for Kor for the fourth season, but the show was canceled after the third season, and he never got his chance to appear again (Kor did appear in TAS: "The Time Trap", but was voiced by James Doohan). Colicos was also the person who gave the Klingons their dark-skinned, mustached look. He said he was going for the "Genghis Khan" look. Makeup artist Fred Phillips agreed on it, and conceived the Klingons in this fashion.  He did eventually reprise his role in DS9: "Blood Oath", "The Sword of Kahless", and "Once More Unto the Breach".
- Colicos was director John Newland's first and immediate choice for the role of Kor. He got the script only two hours before flying to Los Angeles from Toronto, and read it on the plane. 
- Victor Lundin played the tall Klingon lieutenant who returns Spock to Kor's office following the level 4 mind scan. Lundin's character can also be seen in Kor's office reporting the escape of prisoners Kirk and Spock. Victor also appears in a scene as the Klingon which Kirk chokes into submission with a belt cord; followed by Spock's administration of an incapacitating neck pinch. One of Lundin's most notable roles just prior to this timeframe was the part of Friday on the film, Robinson Crusoe on Mars.
- The unknown actor usually portraying Bobby appears as one of the Klingon Guards outside Kor's office at the end of the episode.
- The baldric that Kor wore was reused for Worf during TNG's first season. (Star Trek: The Next Generation Companion (? ed., p. ?)) When it was exhibited at the Smithsonian Institution as part of a Star Trek retrospective in the 1990s, the material could clearly be seen to be burlap sacking, painted gold.
- The same exhibit showed that the buckles of the Klingon belts were pieces of bubble pack, with the bubbles painted silver to resemble metal studs.
Sets and props
- This is one of only two episodes that show an actual Klingon flip-top communicator (shown when Kor contacts his fleet), which is similar to, but smaller than, the Starfleet version. The other episode is "Elaan of Troyius". The communicator was recycled from the Eminian version from "A Taste of Armageddon". It appears that Kor uses "texting" and wireless telemetry – possibly one of the first uses of the now common wireless technology in film/TV media.
- Also recycled and reworked from "A Taste of Armageddon" are the sonic disruptor pistols, first used here by the Klingons and later by the Romulans.
- The boxes in the Klingon munitions dump were spray-painted corrugated cardboard containers.
- The main gate to the Organian village, where Ayelborne greets Kirk and Spock was previously the gate to the Rigel VII castle in "The Cage". The stairs on which Spock and Kirk phaser the Klingon guards are the same set where Christopher Pike battled the Kalar in the original pilot. Location filming for both episodes were done at the "Arab Village" portion of the famous 40 Acres back lot. 
- The entrance of the Klingon headquarters is the same building as the main gate to the Organian village, filmed from a longer distance and different angles. 
- The scene where Kirk and Spock stun the guards and break into the Klingon headquarters was filmed in sunlight using a "day-for-night" filter. 
- The view of the citadel at the beginning of Act One is a stock footage shot of the Citadelle Laferrière in Haiti.  The script specified for a matte painting to be used, but the stock footage shot proved to be much more cost-effective. (These Are the Voyages: TOS Season One)
- Since only the bridge set was used in this and the previous episode ("The Devil in the Dark"), most other Enterprise sets were temporarily demolished to make room for additional swing sets depicting Organia interiors on Desilu Stage 9 in addition to the usually used Stage 10. (These Are the Voyages: TOS Season One)
- The shot of Enterprise hit by magnetic pulses was a stock shot of energy bolts hitting the ship, the corresponding live-action sequences used a buzzing electric effects theme – that would be reused for the Klingon Bird-of-Prey firing effect in Star Trek III: The Search for Spock. The shot of Enterprise firing was also a reuse, this time the white bolts shot out of the ship are said to be phasers, even though in other appearances the same effect represents photon torpedoes. The script, written by producer Gene Coon, specified that the battle shall be depicted using stock footage from "Balance of Terror" and "Arena". (These Are the Voyages: TOS Season One)
- Star Trek: Discovery's first season, which debuted in 2017, retroactively provides further explanation for the aggressiveness expressed by Kirk in this episode by showing the first war fought between the Federation and the Klingon Empire just a decade before. Kirk's "legitimate" complaints against the Klingons include the brutal invasion of Federation territory, the killing of its citizens and the aggressive occupation of entire planets, all occurrences that happened during that first conflict.
- The emblem of the Klingon Empire shown in this episode is replaced by the time "Elaan of Troyius" occurs.
- This is the last episode in which the term "Vulcanian" is used to refer to Vulcans. Both "Vulcanian" and "Vulcan" are used at different points in the episode: Kor uses "Vulcanian" and the Klingon lieutenant uses "Vulcan", both in reference to Spock.
- A comic book published by IDW Comics in April 2007, "Against Their Nature", told this story from the Klingon point of view.
- The Bantam paperback Star Trek: The New Voyages included a story called "Mind Sifter" which described the horrific aftereffects of the Klingon torture instrument on Kirk.
- A reference to the events of this episode would appear in the Star Trek: Deep Space Nine episode "The Sword of Kahless", when Jadzia Dax introduces Worf to Kor, Worf tells Kor he had heard stories about Kor since he was a child including Kor's confrontation with Kirk on Organia.
- Kevas and trillium are later mentioned in DS9: "Trials and Tribble-ations" as a tribute to this episode. Also, a 1970s Star Trek fanzine was named "Kevas and Trillium". (The World of Star Trek)
- The Organians are seen once again in the Star Trek: Enterprise episode "Observer Effect". In that story, two Organian observers visit the Enterprise NX-01 to witness how Humans deal with a silicon-based virus (a long-standing test for many galactic races). In the course of the story, one Organian influences the outcome (in this case, saving three lives), a violation of their rules about non-interference, rules that by this story have been relaxed. The lead researcher also comments that preparations for first contact with Humanity will begin, a process that should take approximately "five thousand years" – the arrival of the Enterprise and the Klingon vessel in "Errand of Mercy" negates that prediction.
- The American synth-pop group Information Society famously used a quote from this episode of Spock saying "pure energy" in their 1988 song "What's on Your Mind (Pure Energy)". These two words were taken from Spock's line towards the end of the episode: "Fascinating. Pure energy. Pure thought. Totally incorporeal. Not life as we know it at all."
- The 2013 video game Star Trek uses this episode's title as a chapter title.
- In the Star Fleet Universe it is explained that the Organians' powers only work within their own star system and thus they were unable to truly prevent large scale wars. Their actions in the episode to stop the Federation-Klingon war were largely a bluff. Eventually they would enlist the Interstellar Concordium to impose order on all of the local races.
- However, TOS comics set between Star Trek II: The Wrath of Khan and Star Trek III: The Search for Spock contradict this. The comics claim that the Organians prevented the two powers from going to war at all. Eventually a war does break out, courtesy of manipulation by Yarnek and the Excalbians. Kirk eventually convinces the Excalbians and the Organians to fight each other, and as the Organians disappear, they lose control over the Federation and the Klingons.
- In the 1970 novel Spock Must Die!, the Klingons envelop Organia with an energy shield in order to neutralize the Organians' abilities to prevent war between the Klingons and the Federation. Eventually the plot is discovered and the shield is disabled, and in retribution, the Organians deny spaceflight capability to the Klingons for a thousand years.
- According to the novel The Sorrows of Empire, the Treaty of Organia was signed between the Terran Empire and the Klingon Empire in the mirror universe during the 2260s, suggesting that a version of the events of this episode also occurred in that universe.
- Story outline by Gene L. Coon: mid-December 1966
- First draft teleplay by Coon: late-December 1966
- Second draft teleplay: 3 January 1967
- Final draft teleplay: 6 January 1967
- Revised final draft teleplay: 23 January 1967
- Additional revisions: 26 January 1967
- Filmed: 26 January 1967 – 2 February 1967
- Day 1 – 26 January 1967, Thursday – Desilu Stage 9: Int. Bridge, Dungeon
- Day 2 – 27 January 1967, Friday – 40 Acres ("Arab Village" backlot): Ext. Organian village, Klingon headquarters entrance
- Day 3 – 30 January 1967, Monday – Desilu Stage 9: Int. Dungeon, Council chambers
- Day 4 – 31 January 1967, Tuesday – Desilu Stage 9: Int. Council chambers
- Day 5 – 1 February 1967, Wednesday – Desilu Stage 10: Int. Kor's office
- Day 6 – 2 February 1967, Thursday – Desilu Stage 10: Int. Kor's office, Klingon headquarters corridors
- Original airdate: 23 March 1967
- First UK airdate: 13 December 1969
The remastered version of "Errand of Mercy" aired in many North American markets during the weekend of 12 May 2007. The episode was heavy in new effects, with unique CG shots of Organia from orbit, replacing the stock footage used to represent other planets including Alfa 177, M-113, and Gothos. The Klingon battle was significantly expanded, with shots of a fleet of D7-class battle cruisers bombarding the Enterprise with blue-colored weapons fire. The Organians themselves were also modified, with more refined computer graphics inserted into the episode that remained true to their original appearance. 
Video and DVD releases
- Original US Betamax release: 1985
- UK VHS release (two-episode tapes, CIC Video): Volume 15, catalog number VHR 2311, release date unknown
- US VHS release: 15 April 1994
- UK re-release (three-episode tapes, CIC Video): Volume 1.10, 13 January 1997
- Original US DVD release (single-disc): Volume 14, 11 July 2000
- As part of the TOS Season 1 DVD collection
- As part of the Star Trek: Fan Collective - Klingon collection
- As part of the TOS Season 1 HD DVD collection
- As part of the TOS Season 1 Blu-ray collection
- As part of the Star Trek: The Original Series - Origins Blu-ray collection
Links and references
- George Takei as Sulu
- Nichelle Nichols as Uhura
- Peter Brocco as Claymare
- Victor Lundin as Lieutenant
- David Hillary Hughes as Trefayne
- Walt Davis as Klingon Soldier
- George Sawaya as Second Soldier
- Bobby Bass as Klingon soldier
- William Blackburn as Organian villager
- John Blower as Organian villager
- Gary Combs as Klingon soldier
- Frank da Vinci as
- Eddie Paskey as Leslie
- Basil Poledouris as Klingon soldier
- Paul Power as Organian elder
- Tom Steele as Klingon soldier
- Ron Veto as
- Unknown actors as
- Unknown actresses as
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- "Errand of Mercy" at StarTrek.com, the official Star Trek website
- "Errand of Mercy" at Memory Beta, the wiki for licensed Star Trek works
- "Errand of Mercy" at Wikipedia
- "Errand of Mercy" at MissionLogPodcast.com, a Roddenberry Star Trek podcast
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"The Alternative Factor"
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"Patterns of Force"