Sticks and Stones
"Mind your own business, Mister Spock. I'm sick of your half-breed interference, do you hear?"
Spock barely keeps from flinching at the words. He is no stranger to prejudice, but he never expected to hear it from Kirk. In all their time working together, Kirk has never once made a xenophobic comment towards him, and has always been quick to counter such comments from others. Spock has begun to think of him as a friend, someone he can trust not to hurt him.
Was he wrong?
"Yes," he murmurs blankly. "Very well, Captain."
Kirk turns, and to Spock's surprise, gives him a look of concern. "You look upset, Mister Spock," he says, as if he has not just insulted Spock's very existence. "Is everything all right up here?"
Spock studies him, puzzled, but his question appears to be genuine. "No problems here, sir," he replies, and Kirk nods.
"Good. I'll beam up shortly with Doctor Korby and party."
He leaves, heading for the transporter room, and Spock watches after him, still trying to make sense of his behaviour. Kirk can at times be overconfident and quick to anger, but Spock has never known him to be cruel. A memory rises, unbidden, of the last time Kirk exhibited behaviour out of character for him, when he was split into two halves.
Perhaps, Spock thinks, he has not been wrong about Kirk after all.
He crosses to the intercom. "Security, Spock here. Status of your landing party?"
"Ready and standing by, sir."
"Have them meet me in the transporter room after the Captain has beamed down."
Something is very wrong here, and he is going to find out what.
Author's Note: I wanted to explore Spock's thought process in this scene, since I find it fascinating how much it says about Kirk and Spock's relationship in just a handful of lines. It shows that Spock trusts Kirk enough to notice that something is off and it's not just Kirk being xenophobic, and it shows that Kirk trusts Spock enough to know that that would be the case. (Especially given the consequences for everyone if Spock doesn't notice something's wrong.)