Star Trek: Elaan of Troyius

On stardate 4372.5, the starship USS Enterprise arrives at the planet Troyius, the outermost world in the Tellun System, to pick up Petri, a green-skinned, white haired Troyian ambassador. He is then taken to Elas, the innermost planet to pick up the Dohlman, Elaan - a beautiful but very demanding young woman who is a member of a royal family. Though powerful herself, it is unclear who the "real" power is on Elas. What is clear is that the ruler or rulers of Elas have made the decision to marry Elaan to a royal family member from Troyius in an effort to secure peace between the warring planets.
Both planets are in a border area between the Federation and the Klingon Empire and are at war with each other. It is hoped that the marriage of the Troyian and Elasian leaders will bring peace to the system and sway their leanings toward the Federation, over the Klingon Empire. It is obvious that Elaan is reluctant to be her enemy's bride, cursing that the arrangement was decided on by the Council of Elas in cooperation with the Troyian leader. Petri's job is to try to civilize Elaan, who is spoiled and arrogant, to the posh and noble ways of the Troyians.
Not long after Elaan's arrival, a Klingon vessel is detected entering the Tellun system and avoids all communication hails from the Enterprise. Captain Kirk is then summoned to Elaan's quarters where he finds Ambassador Petri has been stabbed by Elaan. The ambassador is rushed to sickbay where he refuses to have any more dealings with the girl and threatens to advise his leader not to marry her. The job of straightening her out now falls to Kirk.
While in sickbay, Nurse Chapel asks why Elasian women are so prized in spite of their savagery. Petri explains that if the tears of an Elasian female touch a man's skin, they will be enraptured to her forever. (It is not clear whether this is in fact the case for the Troyian leader.) Elaan does not take kindly to being "civilized" and also tries to stab Kirk. He manages to overpower her and she begins to cry saying she is worried by the fact that nobody likes her. Kirk embraces her and tries to comfort her, but then he is overcome by the biochemistry of her tears.
Meanwhile, one of the engineering crew is killed by Kryton, an Elasian bodyguard, who is secretly working for the Klingons. Kryton sabotages some of the Enterprise's systems and tries to contact the Klingon ship. He is captured, but commits suicide before he can be interrogated. Elaan explains that Kryton was from a noble family and had loved her. The arranged marriage had infuriated him and he sold out to the Klingons, probably hoping to disrupt the alliance so that he could marry Elaan.
Elaan tries to use her new power over Kirk to do her bidding. She suggests that he destroy the Troyian planet, but his ethics and willpower are still stronger than her influence. He orders Dr. McCoy to work on an antidote to counteract the power of her tears. Elaan is impressed by Kirk's resolve and begins to treat him as a loving equal, obeying him when he asks her to go to sickbay (the safest part of the ship). Meanwhile, Mr. Scott discovers Kryton's sabotage and takes the ship off main power. He reports Kryton had damaged the dilithium crystals making it impossible to go to warp or use weapons.
Scotty and Mr. Spock work feverishly to repair the damage as the Klingon ship takes up an attack position. There is little they can do about the threat without dilithium crystals. Kirk, still under the influence of Elaan's tears, manages to pull himself together and bluff the Klingons into thinking the Enterprise is fully operational.
In sickbay, the Troyian ambassador once again approaches Elaan with the royal gifts — a wedding dress and a necklace of large, roughly cut gemstones, saying that they symbolize hope for peace. Elaan accepts and subsequently appears on the bridge wearing the gifts. Spock detects strange energy readings from her necklace. Elaan is puzzled because to her the jewels are common stones — the necklace is of little monetary value on her world. Spock discovers the "common stones" are crude dilithium crystals, which explains why the Klingons are so interested in controlling the system. The stones are quickly delivered to Scotty in Engineering where he utilizes the crystals in the ship's antimatter reactor. Power returns to the Enterprise just before the Klingons attack and the enemy ship is successfully driven off. Elaan is once again puzzled by Kirk's decision to just cripple the enemy ship and not destroy it. She asks, "Aren't you going to finish them off?" To which he replies, "No".
A much changed Elaan is delivered safely to Troyius. Before she departs, Elaan gives Kirk her knife as a memento of their encounter, explaining Troyian women do not wear such things. Later, McCoy appears on the bridge to report that he's found the antidote, but finds that it's not needed after all, because Kirk was even more in love with commanding the Enterprise.