Disclaimer: settings and characters as depicted in BBC series not mine. No money being made. Plot is mine.
A Test of their Defences
Sherlock watched with delight as John smoothly negotiated with his contact for the final access pass they needed to get into the target building. Sherlock had decided in the end that an in-person attack was required, which meant disguises and mimicry and cleverness, all things he enjoyed doing from time to time. They had split up for the last three days, each responsible for running their own contacts, with John also impersonating Sherlock electronically through texts and emails and blog postings to keep Scotland Yard at bay.
Now Sherlock was hiding in the shadows, unable to resist watching his Heart at work. Where Sherlock would have infiltrated through lies and façades, John went as mostly himself – a veteran with a need for particular information. He implied, through his words and gestures that he had fallen on hard times and turned to crime to pay the bills, but never pretended to be anything than a man who lived in a flat and was looking for information. John was not an adept actor, so Sherlock had encouraged him in the strongest terms to stick to the truth as much as possible.
John wrapped up his business, making the exchange after checking the access card on the small reader that he had also 'acquired'. Sherlock watched as the contact slipped away and John waited silently in the shadows for a few moments before heading in the opposite direction. Debating if he should try to pick John up while still in his disguise or if he should just beat his flatmate home and therefore be first in the bathroom, Sherlock waited for a moment longer before moving himself.
It was fortunate he did.
Just as Sherlock was about to sneak up on John for a lark, another shadow detached itself and moved towards his flatmate. A glint of metal in the man's hand proved that his intentions were not benign. He had a knife, short blade, probably foldable, definitely sharp.
Ahead of them both, John sped up a few steps and turned the corner, ducking into one of the many narrow and twisted byways that made Whitechapel the warren it was. Sherlock knew those alleys and byways better than anyone: therefore he knew that John was taking to the rooftops right now, which meant that he had also realised he was being followed. Sherlock watched John's would-be attacker hurry forward, not quite quietly enough, in an effort to maintain contact with his quarry.
It was a moment's work to cut along a parallel alley and shimmy up a down pipe, arriving on the roof ahead of John's pursuer but after his Heart. John was moving away from the edge at a rapid pace, ensuring that he kept low and moved from shadow to shadow as much as possible. Taking a chance, Sherlock fired off a quick text and was pleased to see John pause and then change course as he had suggested. The shadowy figure of John's tail slid over the edge of the roof and spotted his quarry, just as they both wanted him to.
It was over in minutes. John led the man past the shadows where Sherlock was hiding and Sherlock had knocked him cold before he even knew that he'd been attacked.
"Nice moustache," John chuckled, turning back to help secure their catch and search the man for clues. Sherlock smirked at him and twirled an end as he had once seen a 'villain' do on late night telly. John shook his head and rummaged the outer pockets of the man they'd assaulted.
"Nothing, not even a wallet: just some cash and the knife," he sighed, slipping said knife into his own pocket, "Do you recognise him?"
"He's one of Tiny Tim's men. An affiliate of Moriarty's," Sherlock sighed, "Someone's got their wires crossed."
With signs, he indicated that the unconscious man was wired for sound – either broadcasting or recording. Sherlock had located the small device, but had not wanted to disturb it and risk giving the game away. John nodded and pinched his lips shut, standing back and looking carefully around.
"Did you notice if he had a partner?" the question would have been insulting if Sherlock hadn't known it was for the benefit of eavesdroppers.
"He didn't, John, do you really have to ask?" Sherlock put as much disdain and snippiness into his tone as he could, his eyes conveying a different message altogether. He'd missed his John immensely over the last few days and was looking forward to returning to the flat.
"Sorry, I'm sure," John's tone was also at odds with his expression, "We'd best head back to Baker Street. I suppose there's no point in calling the police about this idiot."
"None," Sherlock confirmed, standing up and taking John's arm in his hand, gripping delicately, "Let's go."
John nodded and followed along at Sherlock's shoulder, right where the other man preferred him to be. In silence, they crossed several rooftops before slipping back to street level and emerging on a main thoroughfare to catch a taxi back to Baker Street.
"That really is a disgusting moustache," John shook his head as the taxi rumbled its way down Baker Street, "Blonde doesn't suit you at all."
"No?" Sherlock asked absently, more interested in twining their fingers together in a Gordian knot, "Never mind, I'll take it off when we get home."
"This is as far as I can go, mate. There's a spot of bother up there," the cabbie announced suddenly, "Looks like the address you gave me, too."
John was out of the cab and running towards the fire trucks before the taxi came to a full halt, leaving Sherlock to pay with the cash he'd lifted from the pockets of the man they'd knocked out and left on the roof. It was the least he could do for them, after the threat he'd posed to John.
On the footpath, there was a soggy mess, comprised mostly of cardboard and rags, doused in what appeared to be petrol. From the traces, the lot had been tossed on the front steps of 221 and set alight. Someone had used a chemical extinguisher to put it out, though not before the front door had suffered considerable scorching and the brickwork had been blackened with sooty residue.
"Oh John, dear, it's made a terrible mess," Martha was fussing to Sherlock's flatmate, "I used that fire extinguisher you said to keep handy under the stairs: it worked like a treat, but the front door…"
"That can be replaced, Mrs Hudson," John soothed her, an arm around her shoulders, "Were you hurt at all? Any shortness of breath from the smoke?"
"No, dearie, I'm fit as a fiddle. After Sherlock's shenanigans, this is quite tame," was the vaguely insulting reply, but as Sherlock was in disguise he wasn't able to protest without breaking character. He made a subtle sign to John and then slipped away, getting around to the back of the house and climbing up the down pipe again to the bathroom window. It took precisely 64 seconds to remove all traces of his disguise, shimmy back down to ground level and then around to the front of the house, where the police had finally arrived along with a first response ambulance. John was insisting that Martha be checked over and Sherlock went to collect samples and other evidence before the police could ruin the scene totally.
In the back of his mind, though, he was aware that this had been a test of their defences. Moriarty was looking for weaknesses in Sherlock's life: looking for things to exploit at a later date. They'd weathered the first attempts, but Sherlock would need to spend some time enhancing the security of Baker Street and the people he lived with: and soon.