He doesn't see the mark with his eyes, oh no - it comes up on the tricorder in a string of information: perfect health, slight malnutrition, augment, soul mark - back, black petal [image], raised levels of everything, an unpredictable bomb of a human being.
That last he doesn't get from the tricorder, he can see it just fine from six feet out.
The thing that kills him - really, really gets to him- is that there's no other mark. Just the one matching black brand that marked them as a pair to McCoy's menagerie of ruin.
He's supposed to be the one.
Not mysterious green, or Jim's striking gold mocking him from the other side of a swirling giant, or Jocelyn's pink so much larger than the perfect ring of orange around her little finger. This is the one that's supposed to just be for him. And he's a maniac with unclear motives and an edge like he could flick his wrist and destroy them all.
"Something wrong, doctor?" he asks calmly, eyes like ice.
Yes, McCoy thinks, the problem is that I am a walking disaster if you're what the fates think constitutes a good match.
"You're genetically altered." he says instead.
John, Khan, whoever, and isn't that just great, he hardly knows his name - he inclines his head and smirks just a bit.
"I am."
Somehow, just by sitting on it and curling his fingers into the edges, Khan is making the biobed look like a weapon, and McCoy wants to know just how a person does that with something that is bolted to the wall.
The worst part, he thinks, heart racing in his chest, is that he feels it. Standing in front of Khan is magnetic, it tinges the air and makes him lose track of the security team still in the room - but they're forces doomed if they collide, an electron and a positron set to destroy each other in a flash of light.
Khan looks at him like he wants to take him apart. McCoy is afraid that if he rails hard enough, Khan might move.
He grits his teeth and whirls away from it, and everything goes straight to hell and the bomb goes off with a bigger bang than he could have predicted.
So, fifteen years later when Khan is back on the ship ("We need him, he's the only one who knows anything about all this old weaponry - no I don't want another historian, I'm starting to think those are more dangerous"), he vows to try.