Spock had seen it all before, time and time again. She was beautiful by human standards - by Jim's standards - insightful, and at times even logical. He knew the signs by then; the way Jim looked at her and how she looked back, with dilated pupils and wide eyes, a lopsided grin, and an accelerated heart rate. It was different from how Jim looked at him, but the principle was similar enough to suggest that the two phenomena were related, a hypothesis which was borne out by Jim's own thoughts and words, though Jim had never compared the two directly.

Sometimes it was all an act, an easy facade, but this was not one of those times. Jim was truly in danger. Spock had hypothesized from the very beginning that nothing they encountered in this time could be coincidence, and now he had proof that Edith Keeler was at the core of the divergence that they had gone into the distant past to fix. It may have been too late already, but it was Spock's duty to protect the Captain, even though he knew Jim would not wish for him to act.

So, Spock waited until they were helping out at the Mission, and Jim left to run an errand for Miss Keeler. They both watched him go even after the door had closed behind him. Then, Spock turned to Miss Keeler.

"I am aware that you are pursuing a relationship of a romantic nature with Captain Kirk," he said.

Her head whipped around to face him. She seemed startled by his presence and taken aback by his words. She crossed her arms across her chest and retorted with very human indignation, "I'm not pursuing anything. Jim and I have feelings for each other, there's nothing more natural than wanting to see a little more of each other. What's it mean to you anyway?" She hesitated. "He couldn't have a girl back wherever you come from, he wouldn't!"

"Negative," Spock answered. "However, I find myself obligated to request that you desist immediately and abstain from all unnecessary contact with Captain Kirk for the remainder of our time here."

"What? Why?" she demanded. "I've done everything I can to help you since you broke into my attic running from the cops. I even let you get away with stealing those tools when you should have just asked. What do you want now?"

"It is not a matter of what I want, Miss Keeler," Spock said. "I am not at leisure to discuss the details with you, however I must impress upon you that by all probability your relations with Captain Kirk, if they persist, will cause him significant emotional distress at their inevitable conclusion."

"What's that supposed to mean?"

"It is my duty to protect the captain-"

She cut him off, "I'm not going to hurt him, if that's what you're getting at."

"If you persist in your relations, harm is nearly inevitable. Even if I am wrong in my hypothesis, we cannot remain here forever, as you have already reasoned, and regardless of the circumstances under which we depart, Jim will no doubt mourn your absence."

"You may mean well, Mr. Spock," she said, though she did not sound sure of the assertion, "But even if you and Jim have to go back to wherever you're from, I'm still happier having met him, and I'm sure he feels the same."

"It is illogical," Spock protested, but Miss Keeler did not budge.

Spock entered the captain's quarters without knocking or otherwise announcing his presence.

Jim made no move to acknowledge him. He only said, "I killed her."

Spock was not deterred. "I am equally culpable for her death, as I encouraged you to enable her to meet her fate."

Jim looked up from his desk and shook his head. "But in the end, I made the decision and I carried it out. Dr. McCoy tried to save her, and I was the one who held him back."

"I attempted to warn her not to continue to pursue relations with you, but she refused. If only I had been able to better elucidate the circumstances, I may have been able to spare you at least a part of this," Spock said.

"No," Jim exclaimed and stood up from his desk for emphasis. "I know you meant well, Mr. Spock, but despite everything that happened, I can still treasure the time that I had with her and I wouldn't trade it for all the ignorant bliss in the galaxy."

"But sir," Spock began to protest.

"If I died tomorrow-" Jim interrupted, stepping towards Spock as he spoke.

Spock cut him off, "I will not allow that to happen!"

"But if I did," Jim insisted, taking another step closer, "Would you prefer we had never met? Would you wish we'd had less time together, or would you treasure every moment?" He reached out and put a hand on Spock's shoulder.

Spock considered the unpleasant possibility and chose his words carefully, "I will always choose to have more time at your side."

Note: I want to thank oracledivin on Tumblr for the prompt that inspired this fic! This is actually the first of two responses - this one fits the prompt itself, but deviates a bit from the song because of how I see Kirk and Spock's relationship, so I wrote an additional response ("Mary") that features Sherlock Holmes and Dr. Watson instead, but sticks a little closer to the song.

I'm accepting prompts at vtsuion dot tumblr dot com!