"Spock, stop! STOP!" Nyota cries desperately. "He's the only way to save Kirk."
For a moment, it seems as though Spock will not be able to restrain his rage. There is murder in his eyes, pure and savage. This must have been what his ancestors looked like, once upon a time - the naked emotion, the blatant thirst for blood. Then, her words register, and he goes utterly still. "Explain."
"Dr. McCoy thinks that Khan's blood can bring him back. But he used up all of the sample he took in his experiments, so we need to take more."
The thought of allowing the monster beneath him to continue drawing air nearly brings Spock physical pain. Everything that has happened in the last forty-eight hours has been a result of this abomination of a man, and that cannot go unpunished. Yet to exact retribution now will surely end all hope of ever recovering the captain, and that is not a path Spock ever wishes to walk. Jim went against the Prime Directive because he was Spock's friend, and Spock did not understand the sacrifice he was willing to make at the time, but he is fully cognizant of it now, and he is a Vulcan changed. He can do no less than sacrifice the ancient need in his warrior's blood to save Jim.
"Kirk," Khan breaks in, his voice winded from the pressure Spock's weight puts upon his lungs, "he is injured?"
With no little satisfaction, Spock notes that bearing down upon his captive's chest is enough to render him silent, but not enough to suffocate him fully. "My captain is dead, Khan. And you, it would seem, are the only available avenue to bring him back to us. It is for this, and this alone, that I will suffer you to live. You asked me how I could be expected to break bone when I could not bring myself to break the rules, but you see, our orders were to execute you upon sight. If breaking a few bones is necessary in order to see that done, I believe you will find that I can do it very easily now. If you wish for your life to continue, you will come with us, and you will allow us to take the blood my captain needs for a transfusion."
There is just enough breath left in Khan's lungs for him to offer his surrender, and he does so whole-heartedly. Spock knows better than to trust in it. He has seen what happens when this man surrenders.
Even so, he rises, pulling Khan along with him.
"What has been done with the captain in the interim?" Surely something has been done to preserve his brain functions. As soon as Kirk breathed his last, Spock had him beamed straight to Sickbay, vainly hoping that he could be revived. Inevitably, Dr. McCoy pronounced him dead upon arrival. How long had it been between that moment and this madcap scheme occurred to the good doctor? Had it been longer than six minutes? Whatever the case, Spock will still take the chance given to them. Perhaps the transfusion will be enough to negate the possible damage to Jim's neural pathways.
Nyota glances at Khan warily before admitting what Dr. McCoy had done. Their captive is expressionless, belying no hint as to his thoughts on the matter. Either way, Spock cares little. The man's comrade is still reasonably well preserved. It is enough.
"There's supposed to be a shuttle coming for us in a few minutes," Nyota reports. "We didn't have enough power to transport anyone back to the ship."
Spock wonders if it is wise to discuss such things in front of Khan, but he says nothing. As soon as they have the blood they require, Khan will return to the brig, and nothing short of Jim's express orders will convince Spock to remove him. He finds such an eventuality unlikely.