A/N: Field Medicine III is the last of the chapters on this subject, at least in this part of the story. The next one in the series follows straight on from this one. Having done some research, Commander Nelson's rank is the equivalent to a Lieutenant in the British Army; this is one rank below John, and is why she salutes him first and not the other way around. I thought it would be nice to introduce an interesting and intelligent OC, as well as fleshing out Gregson a wee bit. The next chapter will be from someone else's third person point of view, though I decided to write this chapter in the third person for story-flow reasons.

Screaming along the flyover at breakneck speed, blues and twos broadcasting the emerging crisis to the surrounding high-rises, Greg turned the wheel sharply and careened around the corner into the red brick terrace. Will Gregson was pale beside him, knuckles white on the handle to the left of his head as the saloon screeched to a halt. The street was a mess of rust-coloured dust and debris, and the smashed glass crunched under their feet as they stepped gingerly across the no-man's land created by the gas explosion manufactured in their latest murder scene. Although very few actual residents had been home, all the civilians having been asked to leave while SOCO did their stuff, it was clear that the Yard and the local nick at Golders Green had taken a hit. James summed it up, Greg's stomach swooping as they took in the blood and chaos before them.

"Shit. How many were bloody well in there?"

Detective Sergeants Manerjee and Cooper were waiting for them at the 20-metre cordon.

"No dead so far, we're waiting for confirmation from the doctor on scene on how many critical and majors we've got."

"Yeah, speaking of-where'd you lot find 'im? He's a demon, he is." Manerjee interjected.

Greg and Will spoke in unison, looking to one another with their brows wrinkled in confusion.

"Doctor?"

"Oh...of course!"

Greg's shaking finger pointed to a lithe, blue-coated form with a shock of madly curly hair, perched on a wall beside a shaky young copper, holding his arm rigid as Chris Anderson neatly splinted it, before sprinting off in the direction of the arriving ambulances.

An LAS commander came up beside them, Sherlock meeting the small knot of men at the next line of blue tape. "There's an Army medic on scene currently in the process of triage. He knows what he's doing, so if you wouldn't mind deferring to him, perhaps we can get these people out of here more quickly."

To a bystander, Sherlock's snapped message would have seemed like a peculiarly savage shock reaction. Thankfully, that particular paramedic had met Sherlock before, and was able to take it all in her stride. To Greg and Will, who knew the two men better, the pride underlying the irritable statement was unmistakeable.

"Doctor Watson's on form, then. Good, he's exactly what we need," murmured Greg.

At Will's raised eyebrow (the thought of the small man leading a company of strangers and co-ordinating the rescue effort being just on the wrong side of believable), Greg smiled.

"You've not seen John at work before, have you? Just because he looks like a softie, doesn't mean he's not fully battle-ready."

As Sherlock led them up to the last cordon at the epicentre of the blast, they caught sight of John. He was moving quickly from person to person, only stopping to shout instructions to the uniformed and plainclothes officers in the area. Some were bent over their colleagues, monitoring their vital signs or holding their hands; others were taping off evidence sites or comforting the walking wounded and sitting blankly on the adjacent garden walls. PC Cumming let out a groaned expletive as the man he'd been checking (a DC Shukman from the local nick), went limp underneath him.

"Aw, fuckin' hell. DOC! He's not breathin', what do I do again?"

At Blair's calm but urgent shout, John's head turned sharply. Running over, he knelt at the other side of the bleeding man. The hair at the nape of Greg's neck stood on end, Will frozen in place, as the same Captain's voice carried across the open space. Blair's back was ramrod straight, head cocked to one side as he took in John's instructions and watched him scissor his hands and press on the patient's chest at a phenomenal rate.

Watching John doing CPR was like watching a sniper take shots at tin cans. Each ad every downward thrust was completed with enough power and precision to take Will's breath away, and all four coppers stood back in wonderment as John snapped backwards and Blair forced air into his comrade's lungs.

John indicated that Blair should continue it until the paramedics could take over, nodding approvingly as the young man pumped the patient's chest at comparable speed. Standing up in one fluid motion and looking directly at the paramedic, John smiled grimly.

"Commander Nelson? Dr John Watson, formerly Captain Watson, RAMC."

Nodding and surveying the carnage with watchful eyes, Rosaline spoke crisply. "I had sort of guessed that, sir. I'm quite good at recognising ex-forces when I see them, especially the higher-ups." Rolling up her sleeve, she revealed a tattoo of Asclepius' rod, wound around an anchor and bordered with a diamond shape.

"Sub-Lieutenant Rosaline Nelson, formerly Royal Naval Medical Service. And no, before you ask, no relation to that Nelson. I'm nowhere near that good at avoiding shrapnel, else I wouldn't be here instead of on the water."

Wincing in sympathy, John stood up straighter, receiving the four-finger salute with a respectful straight-fingered one of his own. "Right. No dead as yet, four critical including the one currently being-er, make that just breathing and no more. Four critical, seven majors including two internal bleeds, two shockwave fractures, one nasty head wound, a pelvic fracture and a partial amputation, which I've already stabilised. Shall we?"

Spreading his hand to indicate the scene, John led the commander to the makeshift field hospital set up on the waste ground across from the last of the houses in the terrace. White SOCO tents had been placed together, with each type of casualty grouped under a sheet scribbled with a block of colour. Criticals had been left in situ, labelled with red sheets, majors had been evacuated and grouped under an orange banner. The more minor injuries and walking wounded, including the broken arms, concussions and fractured ankles, were huddled in the last tent under a blue banner and illuminated by the floodlights, blinking owlishly as Nelson directed the teams of paramedics through the regimented melee.

"You did all this in twenty minutes?" Will whispered as he stood, mouth agape, while the critical and majors were spirited out into the waiting ambulances and choppers. Blair appeared at Greg's right shoulder, shoulders squared and face set.

"Sir. Sir, ma'am. Sarge, Mr Holmes." Nodding to each of them in turn, the constable inclined himself in John's direction, then grimaced as he caught sight of the middle-aged SOCO with the deep arm wound. "Captain?" John's head swivelled, and Will took a closer look at him in the thick of it.

"Yes private, ah-sorry-Blair?"

Brow crinkling, the PC stood up straighter. "S'okay, sir. My brother said you might do that. That thing you did, to the guy with the glass in his arm..."

He shuffled his feet, looking distinctly uncomfortable.

"It's okay, Blair. Think you've earned the right to ask, given that it was you who got Shukman breathing."

"Is that what you did to Cam? So they didn't have to take so much of 'is arm off?"

Surveying the lessening hubbub, John nodded, looking dreamily at a point somewhere over the heads of the assembled throng. "Sort of. That guy's injury was a shrapnel wound, a lot cleaner than an IED injury. No less severe though, and no less bloody painful." The last part came with a sideways look at Nelson, who smirked and directed her subordinates through the complex, ticking each casualty off on John's triage matrix as they passed.

Draped in bright orange shock blankets, the three men were gently herded into Greg's car as Gregson stood behind to begin the cleanup. Nodding to Nelson, John turned to leave, Sherlock falling into step behind him as Blair walked alongside, holding the door open before folding himself into the passenger seat.

Will shook his head at the retreating backs, wondering just what it would take to throw Sherlock Holmes and Dr Watson off their stride.