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Tear Jerker: Star Trek VI: The Undiscovered Country
The Klingon Chancellors death is surprisingly tearjerking.especially when you consider people in both Star Fleet and the Klingon Empire worked TOGETHER in order to assassinate him. Because they didn't want him to make an alliance between their two governments!
His last words are heartbreaking: "Don't let it end this way, Captain..."
"Second star to the right...And straight on til morning." Manly Tears were shed.
More like a Fridge Tearjerker, but how Valeris' betrayal affects Spock. She's second only to Saavik when it comes to Spock's proteges. He tried his best to teach her how to have hope, but she wasn't good enough to live up to it. She didn't just betray him as a Starfleet officer, she didn't just betray him as a Vulcan, she betrayed him as a surrogate daughter. That's a hard blow for anybody.
Her betrayal gets him openly angry, causing him to smack the phaser out of her hand. Meaning that he's angry enough for it to crack that Vulcan calm. Oh yeah, he is PISSED, and it is tragic, because it means that he trusted her that much.
And then he's still horrified after being forced to dig the conspirators' identities out of her mind. These sequences feature some of Nimoy's best acting in the whole franchise.
The fact that among the conspirators was Admiral Cartright, a relatively minor (though friendly) character who had previously appeared in one of the more popular Star Trek films may come as a slap in the face to some fans.