Lord, please let us live. And if we can't, please let us take this insane bastard with us.
He's moving before the gun fires, adrenaline transforming his watery human muscles into coils of unadulterated power. He's too busy using them to notice. In less than a heartbeat he has Sherlock by the jacket, his grip shackling the pair of them together for whatever comes next. Sherlock can calculate like a super computer, throw a punch like an MMA star, but John is the one who knows war, and what they do now will be his call.
His body has already made that call, skipping his brain entirely in favor of instinct and training so hard won that it belongs to him on a cellular level now. They are moving away from the explosion, away from the pool, towards the shelter of the corridor and its promise of escape, before John's conscious mind has registered that the explosion is not where he expected it to be.
Sherlock hadn't shot the vest yet.
John knows that in reality you can't outrun an explosion, not the way the people do on telly. The heat, the sound, the shock wave are governed by the immutable laws of physics, and they will have their way. For just this second, though, the laws of physics are on their side; partially because walls are thicker than air, partially because there is a large body of water near to hand, but mostly because it wasn't the vest that went up. It was a smaller, more controlled charge, originating a floor higher and on the opposite side of the pool, distracting Moriarty and temporarily occupying the bevy of snipers that had so complicated their situation. It was quite possibly the only thing that could let them escape with their lives.
Moriarty has stationed a pair of guards in the corridor, men well-trained enough to hold their position with the sound of the explosion snarling through the building. They aren't actually expecting anyone to escape, though, and John and Sherlock make short work of them, a single hit apiece, barely slowing their mad dash as a second small explosion rocks the walls. In a distant, detached corner of his mind John is intensely grateful that his flat mate is not an Ivory Tower sort of genius. Scattered gunshots are discernible amid the echoes from the pool, and any second now the inevitable will happen and they must be out before the Semtex goes...
The doors are open, cool night air that he never again expected to taste sliding into his lungs, when the world explodes. Even at this distance the force is enough to send him sprawling, stunned and deafened, a barrage of flaming stones pelting him and the air ripped from his lungs. His vision goes black and for a long, long moment it is all he can do to hold his mind and his body together. Breathing is too much to ask. Eventually an urgent message works its way back to his medulla; the reply is a muscle spasm in his chest that wrenches his lungs to unwilling function. He coughs and gasps and coughs again, searing pain blooming between his ribs and stabbing across his skull. Something broken in there. Multiple things, perhaps. But if the pieces are a little cracked, they are at least still attached to one another, and none of them seem to be on fire. Not literally, anyway. Overall, that's rather better than he had any right to expect.
He still can't hear anything, but after a few blinks his dry and aching eyes confirm the presence of a sprawled body on the pavement beside him. The light from the inferno that was once a pool, while bright, is too irregular for him to tell if that body is breathing or not, so John negotiates with his arm until it moves, stretching out to brush awkwardly against Sherlock's face. His fingers trail down, pressing firmly as they round his friend's jaw and seek out the carotid pulse. It's there, and John's arm goes slack for a while in celebration.
The next thing to register is a bank of flashing lights- police cars and fire trucks. Rather a lot of them to appear out of thin air, so he must have blacked out for a bit after all. Someone is touching him, running hands along his limbs and torso, checking for breaks. He's just coherent enough to expect it when he's rolled and strapped onto a gurney. The swift, efficient motion is dizzying; they're almost to their destination before the world stops spinning enough for John to once again process what he sees. He's being bustled into an ambulance; Sherlock is meeting a similar fate a few meters away. Everything is blurry and surreal - the paramedics with their silent, moving mouths, the shimmering jets of the fire hoses, the fluid mosaic of police in bright vests spreading out to encompass the flames. His last glimpse, however, as the oxygen mask descends and the doors close, is startlingly clear: two men standing together, one with salt and pepper hair and a hovering cloud of waiting attendants, the other tall and imposing, with only a single assistant and an umbrella still furled despite the damp. Their identical expressions are bathed half in red and blue flashes, half in firelight. They watch anxiously as he and Sherlock are whisked away from the rush and the panic, hopefully to somewhere sedate, with a security staff and morphine. There's already a line in John's arm, which might explain the sudden heaviness in his eyelids. He wonders, briefly, if there isn't something else he has to do before the darkness reclaims him; a momentary panic speeds his heart. Then he remembers the two men watching, and he calms again. He and Sherlock are both alive. His turn is over with. They can take it from here.