“Day of the Dove” begins with a landing party on a barren planet, investigating a distress signal from a Federation colony that now seems to have completely vanished. Meanwhile, the Enterprise detects a Klingon vessel heading their way, and the landing party quickly concludes the colony had been destroyed by Klingons.

But after responding to a distress call the Klingon ship has been attacked and disabled, with heavy loss of life, and its armed landing party suddenly appears on the planet to take the Enterprise crew hostage. The Klingon captain Kang (Michael Ansara) accuses Kirk of attacking him with a new Federation weapon, and claims the Enterprise in compensation for his disabled ship.

“Go to the devil,” Kirk says.

“We have no devil, Kirk, “Kang responds. “But we understand the habits of yours.”

Chekhov suddenly goes berserk (not for the last time), desiring to avenge the death of his brother, killed by Klingons. Kang uses a device to torture him until Kirk relents (with Chekhov screaming, ”Don’t let these animals have the ship!”) and arranges to have them all beamed aboard the Enterprise. But he secretly signals Spock, and the landing party is beamed aboard, while the Klingons are kept in the pattern buffer until Security is ready.

But also aboard the ship is the Alien Entity, defined so far only as a shimmer of light.

Because the Klingon ship is spewing radiation, the Enterprise beams its remaining crew over, so a total of 38 Klingons are aboard. At this point, the apparent coincidences accelerate---along with the Enterprise, which is suddenly bolting for the edge of the galaxy at warp 9. It is also attacked from nowhere, trapping 400 crew members beyond sealed bulkheads. Now there are also 38 on the Starfleet side.

When both sides confront each other, their modern weapons disappear and are replaced by swords. The alien light appears pleased when they fight.

But there’s another clue to the accelerating blood lust and racial slurs when Chekhov runs from the bridge still intent on avenging his brother, but Sulu tells Kirk that Chekhov doesn’t have a brother.

Spock locates the alien force. “We must contact it,” Kirk says. “See what it wants.” Spock theorizes that it can manipulate both matter and mind. But to what end?

Kirk decides to defuse the hostilities with Kang, to “bury the hatchet,” which Spock points out is an apt phrase given the circumstances.

But there’s another burst of war fever and racism on the bridge. Scotty calls Spock “ a green-blooded half-breed freak” among other things, and McCoy joins in. Spock says he’s not so pleased about being around humans either.

“What are we saying?” Kirk says. “What are we doing to each other?”

“This is war!” Scott cries.

“There—is—no—war,” Kirk says. “We’ve been trained to think in other terms, to fight the causes of war if necessary. Has the war been staged for us—complete with weapons, ideologies, patriotic drum-beating, even race hatred?”

Spock agrees, and hypothesizes that basic hostilities between humans and Klingons have been magnified---that they are to fight apparently by design.

Meanwhile, a rampaging Chekhov has trapped Kang’s wife (who is also his science officer) and is in the act of trying to rape her when Kirk intervenes. “Is this what’s in store for us? Violence? Hatred?”

Dr. McCoy—who has been railing against Klingons as butchers—reports that everyone’s wounds are healing. It appears that the entity will heal them so they can continue fighting, perhaps forever.

McCoy then apologizes to Spock for his racist outburst earlier.

“I, too, felt a brief surge of racial bigotry,” Spock says. “Most distasteful.”