He doesn't know if it's going to work.
Sickbay's a mess, filled far past capacity because the Enterprise isn't a warship, goddammit, and wasn't built to handle the casualties of a full-out attack. Leonard's in five places at once, shouting orders to M'Benga and the nurses and trying to not let Jim's cryo tube get out of his sight for more than a few moments at a time. He doesn't know what's going on outside Sickbay, but at least it doesn't feel like they're falling anymore. Security's watching the soldier they unfroze, who's currently doped up on more sedatives than Leonard's ever given anyone in his life, because they've all seen what Khan can do and they're not taking any chances with his crew.
"Doctor McCoy!" Sulu's voice barks over the nearest communications unit. Leonard practically vaults over a gurney to reach the button.
"That hobgoblin had better have Khan alive," McCoy snaps, because dammit, Jim's frozen and dead and who knows how much time they still have –
"They're transporting directly to sickbay now."
Leonard snatches the nearest IV drip as the transporter activates near Jim's pod. The second Khan materializes – out cold on the floor, and damn, he never wants to be on the receiving end of Vulcan rage – Leonard jabs him with a hypo of the strongest sedative he has. He ignores Spock and Uhura entirely as he draws two samples of Khan's blood and then inserts an IV drip with more sedatives. He's taking absolutely no chances with Khan's altered physiology.
When he looks up, Uhura's gone – probably off to the bridge to hail Starfleet and find out what the hell's going on – and Spock is inspecting the cooing tribble on his desk. Leonard falters. Spock looks exhausted, his uniform and hair uncharacteristically out of place, and there's a shattered look in his eyes when he glances at Jim's cryo tube.
"This is illegal," Leonard says, fingers hovering over the buttons that will defrost Jim, and fuck it all, he's said it.
This is illegal.
It's an untested, unknown thing that he's about to put in Jim. It's Khan's blood, but it's something else too, and no one knows why or how it made a goddamn tribble come back to life. There could be horrible side effects. It might not even work on a human.
He's about to break a few dozen medical and Starfleet codes, and he's terrified that it won't work.
Leonard realizes his hands are shaking. He puts Khan's blood down and drags his hands over his face, fighting back the bizarre urge to laugh. He can't fall apart now, because Jim. Spock steps to Leonard's side and hesitates for a fraction of a second before placing his too-warm hand on Leonard's shoulder. Which is weird.
"In very rare cases, Doctor," Spock says quietly, "The needs of the one are necessary to ensure the well-being of the many. This – appears to be such a case."
Leonard stares at Spock for a full thirty seconds.
"Goddammit, you pointy-eared hobgoblin, it's not that hard to say 'I've got your back if this all goes to shit,'" Leonard growls, but Spock's support warms him enough to jar him out of his panic. He punches in his medical override and watches the cryo tube start to defrost.
Khan's blood feels heavy in his hands. It might not work, but goddammit – Leonard has to try.