TOS Season 2 Episode 10 Journey to Babel

Enterprise, under the command of Captain Kirk, is transporting Federation ambassadors to a conference on the planet Babel to discuss the admission of the Coridan system into the Federation. The system is a prime source of dilithium crystals, but is underpopulated and unprotected, a situation that some would prefer to maintain by keeping Coridan out of the Federation.
Sarek, who is a Vulcan ambassador, boards the ship with his human wife Amanda, ignoring Spock's greeting. Captain Kirk learns that Sarek is in fact Spock's father, now estranged because he had disapproved of his son's decision to join Starfleet rather than attend the Vulcan Science Academy.
During a reception for the passengers, the Tellarite ambassador, Gav, demands to know Sarek's position on Coridan. Pushed for a response, Sarek refers to the need to protect Coridan from unauthorized mining operations, with which Tellarite ships have been involved. Gav takes offense at the allegation and the confrontation briefly becomes physical before Kirk intervenes, warning all parties to keep order on his ship.
Meanwhile, Communications Officer Lt. Uhura has detected an encoded transmission beamed from Enterprise to a fast-moving vessel at the extreme edge of sensor range. Shortly afterward, Ambassador Gav is found murdered, his neck broken by what Spock describes as an ancient Vulcan method of execution called Tal-Shaya, casting suspicion on Sarek. During questioning, Sarek suffers a cardiovascular event, and is rushed to the sickbay, where Chief Medical Officer McCoy determines that he requires immediate surgery. Because there is a shortage of his rare T-negative-type blood, Spock volunteers to donate some of his own blood for the operation, using an experimental stimulant for increased blood production.
Plans for the procedure come to a halt when Thelev, a member of the Andorian delegation, stabs Captain Kirk. Kirk subdues Thelev but is seriously wounded and taken to sickbay, while Thelev is imprisoned in the brig. In accordance with regulations, and despite Amanda's emotional plea, Spock refuses to continue the blood donation and turn command of Enterprise over to anyone else, as the situation is too critical.
Hearing of Spock's refusal to relinquish command, and having recovered sufficiently to be able to walk, Kirk returns to the bridge to relieve Spock and order him to the sickbay, intending to turn command over to Mr. Scott. When Uhura picks up another encoded transmission from inside Enterprise and traces the source to the brig, Kirk decides to stay on the bridge. When Thelev is searched, it is discovered that one of his antennae is fake and conceals a small transceiver.
The unidentified vessel closes in to attack, moving too quickly for Enterprise to lock phasers. The ship takes several hits from the attacking vessel. McCoy begins the operation on Sarek, who is receiving blood directly from Spock. Kirk orders Thelev brought to the bridge and questions him about himself and the attacking ship; Thelev is unresponsive. Kirk decides on a ruse, shutting down internal power to make Enterprise appear crippled. The attacker approaches, and Enterprise damages it with a surprise phaser attack. The disabled ship self-destructs, and Thelev reveals that both he and the ship were on suicide missions; he then collapses and dies from a delayed-action poison.
Kirk returns to sickbay for further care and finds Spock and Sarek both alert, the surgery an apparent success. Spock speculates that Thelev and the attacking ship were of Orion origin, and the speed and power of the latter were consistent with a suicide mission, with all energy dedicated to attack. Thelev's mission aboard Enterprise, Kirk and Spock presume, was to sow distrust among the Federation members and weaken Enterprise prior to the attack. In support of this theory is the fact that Orion has been raiding Coridan, and would profit by selling dilithium to both sides in a war. Amanda asks Sarek to thank Spock for saving his life, but Sarek shrugs and says that it was only logical. Amanda expresses anger at this harping on logic, and Spock, noting his mother's exasperation, asks Sarek why he married her. Sarek replies, "At the time, it seemed the logical thing to do," and offers Amanda his hand in a ritual gesture of affection. McCoy then firmly orders Kirk and Spock to remain quietly in bed, finally getting the last word.