The empty house on the other side of Baker Street was a lucky break. From here, Sherlock has a perfect vantage point of the whole block. There's no way into the building from the back; anyone looking for a shot at John will have to approach from the street. And if tranquilizer darts are still the weapon of choice, then it will have to happen in the flat.
Sherlock crouches down in front of the window and checks the sight on his sniper rifle. Thanks to the vestiges of his connections and a few straggling outstanding favors, they were able to transform the last of their money, both their laptops, and a handful of questionable promises into this rifle and a Sig Sauer P226R for John. Sherlock would have traded his coat for the look in John's eyes when he turned that gun in his hand. He makes a mental note to make sure John always has the latest army issue firearms, particularly those banned on British soil.
He waits for the light to come on in 221B. And then he'll wait some more. Moran's people might not even come tonight, but Sherlock thinks they will. If Moran believed his texts, he'll want to strike while the opportunity is open.
The last time John walked away from 221B Baker Street, he was not at all sure he would ever return. He figured eventually Mrs. Hudson would insist that he come and clean out the flat, and at that point he'd either do it, or else he'd tell her to just throw it all out, all of it, and be done with it. She never asked. He now suspects that's because Mycroft has been paying the rent.
He stands in front of 221A and raises his hand, then lets it drop at his side. It's embarrassing, but the truth is he's a horrible liar, just like Sherlock always says. It's not even that he's such a moral person. He really doesn't have a problem with lying to serve a greater purpose like, oh, for example, saving his life and restoring Sherlock's. It's just that he's so bad at it. Still, it's what needs to be done. He raises his hand again and knocks.
Mrs. Hudson opens the door and gasps. One hand flutters to her throat and the other reaches for him and pulls him inside. Her flat smells like it always has done, of tea and baking and herbal soothers, and it's bathed in that warm yellow light that he remembers.
"John," she says, "oh, John, it's so good to see you! How are you?"
"Hullo, Mrs. Hudson," he says fondly, "I've really missed you." And that part is not a lie. "I've come round… I'm so sorry for the interruption, I know I should've called first, but I thought I just needed to come straight here while I had my courage up. I've come to go through the things. In the flat. Like I said I would."
"Oh, John." She hugs him so tightly that for just a moment he feels confused, like he's dreamed all of this and actually Sherlock's still dead, he's still all alone, and Mrs. Hudson feels sorry for him because his heart is breaking all over her kitchen floor. His chest constricts like he might cry. Mrs. Hudson hears the hitch in his breathing and hugs him even tighter.
"Hrm." John makes a little noise in his throat and shakes his head. It's not a dream and he's got an ache in his pectoral muscle and a strange little mark from the tranquilizer dart to prove it. Sherlock is alive and just across the street. He suddenly realizes that when you count all the times John thought he was alone and was actually being followed by Sherlock, this is the farthest away he's been since the night he appeared in John's flat. It's uncomfortable. When this is all over, and they find their lives again, and John goes to work or to the pub, and Sherlock gallops around the city being Sherlock, they won't be within whispering distance of each other at all times. Not very often at all, in fact. That will take some getting used to.
He clears his throat. "I'm very sorry, Mrs. Hudson. I know I should've come ages ago."
"Oh don't be silly, dear. It's alright. This isn't easy. I've just been so worried about you."
"Thank you, I'm really doing fine."
"Are you?" She arches an eyebrow. "You look…"
"I know." He looks like hell on a bad day. He snuck into a gym earlier so he could at least take a shower, but he hasn't shaved in weeks. His clothes were disgusting and his pack got left behind in Peckham, so he stole some clothes from the locker room and they're too big, exaggerating how thin he's become. He looks truly terrible.
He squares his shoulders and straightens his back, trying for the expression of a brave soldier marching to his death. "Mrs. Hudson, I hate to ask you this, especially since I just came barging in without any warning, but I… This is going to be… difficult for me, and I… Well, I … I would really appreciate some privacy while I'm upstairs. Perhaps you could go sit with Mrs. Turner for a bit? I am so sorry to ask."
"John." He closes his eyes so he doesn't have to look at her face; her voice is bad enough, so full of warmth and sympathy. "Of course. Take as much time as you need. I was just thinking of going for a pint, actually. Let me just get my coat…" She pauses. "Are you sure you wouldn't like some company? I can be down here just in case. I'd hate to –"
"Please, no. I really would appreciate it."
"Of course."
"And Mrs. Hudson? When you come back, just please… No need to look in on me."
"I won't bother you, dear."
She lets John into 221B and leaves. He sighs with relief and climbs the stairs.
Memories are flooding back with each step (how could there be so many in really such a short time?) but there is no time for that now. John flicks on the light in the living room to signal Sherlock that he's arrived, and goes back downstairs to set up the trip wire.
"Sir. He's entered the flat, alone."
"Still no sign of Holmes?"
"Last report was at Bromley this morning, 0500. Watson's been on his own all day, sir."
"It's early yet. Stand by; we'll take up positions in about an hour, on my mark. Haque and McMann, with me. Ayres, you'll cover us. Lewis, east route. Chen, west. Clear?"
"Yes, sir."
"If Holmes shows up, shoot to kill."
"Yes, sir."
"We take Watson alive."
"Yes, sir."