"Day of the Dove" is the seventh episode of the third season of the science fiction television series, Star Trek, first broadcast November 1, 1968, and repeated June 17, 1969. It was written by Jerome Bixby and directed by Marvin Chomsky.

In this episode, an alien force drives the crew of the Enterprise into brutal conflict with the Klingons.

The Federation starship USS Enterprise responds to a distress call from a human colony on Beta XII-A, but on arrival finds no signs of any type of inhabited settlement. A landing party, including Captain Kirk and Ensign Chekov, beams down to investigate further. A few moments later, they are found and surrounded by Klingons who have transported to the surface from their own orbiting vessel. Commander Kang accuses the Enterprise crew of firing upon their vessel and demands that they surrender immediately. Suddenly, Chekov makes a move to attack the Klingons, claiming that they had killed his brother Piotr. Kang's men subdue him and use an agonizer device to torture him, forcing Kirk to agree to surrender. However, upon contacting the ship, Kirk surreptitiously warns First Officer Spock after asking to be beamed up. Spock uses the transporter to materialize the Enterprise crewmen first, followed by the Klingons, who have been brought aboard without their weapons. Kang surrenders and he and the other Klingons are escorted to secure quarters on the ship.

Meanwhile, a glowing entity composed of pure energy, which had initially emerged on the planet below, enters the Enterprise undetected and interfaces with its controls. The ship lurches into warp at maximum speed headed for the edge of the galaxy. With the crew panicked, the entity then causes various bulkheads on the ship to open and close, using the element of chance to isolate small groups of the crew and the Klingons in close quarters. With tempers high - and spurred on by the sudden materialization of swords and other combat weapons - they begin to fight. Spock soon discovers the presence of the entity, apparently feeding off the desperate, violent emotions which are surfacing. When informed by Lt. Sulu that Chekov never had a brother and is an only child, Kirk realizes that the entity is capable of implanting false memories in order to trigger aggression. Kirk and Spock try to calm the crew's escalating furor to no avail. Kirk believes that if he can get to Kang, the Klingon commander can help stop his crew from fighting and help return the ship to a normal state.

...
Wikipedia