How we cite our quotes: All quotations are from Star Trek II: The Wrath of Khan.
Quote #4
SPOCK: The prefix code?
KIRK: It's all we've got.
It always pays to have an ace in the hole out in space: in the kind of game they're playing, they're playing for keeps.
Quote #5
KIRK: Khan, how do I know you'll keep your word?
KHAN: Oh, I've given you no word to keep, Admiral. In my judgment, you simply have no alternative.
You can sense the battle of wits and wills here: Kirk with a little surprise waiting for his enemy, Khan convinced that he's finally gutted out a win after fifteen years. It's a deadly game, but it's still a game, and to paraphrase Kirk, neither of them likes to lose.
Quote #6
JOACHIM: They've damaged the photon-control and the warp drive. We must withdraw.
KHAN: No! No!
JOACHIM: Sir, we must! The Enterprise can wait. She's not going anywhere!
Wow, somebody doesn't like letting go, does he? Even when it's in his best interests. On some level, Khan's in this solely to win…to show Kirk who had "beaten" him at long last.