Next we have a beat that's totally unexpected. What could be in Sherlock's bedroom that he doesn't want anybody to see? If he were a normal bachelor, a lover would be the first thing that comes to mind. Since he's Sherlock, it's the last. Jeannie -- the bridesmaid who flirted with Sherlock last week -- comes strolling out. She's tossing around nicknames (Sherl, Mike...) for the Holmes brothers and John is just stunned. So are we. Though we quickly suspect there must be an ulterior motive.
Sherlock tries to get John to focus on the Magnussen case, but he wants details about Jeannie. It's like the show is trying to switch focus and tone from last week's rom-com to this week's thriller, with John still stuck in the previous mode and Sherlock wanting to get back to a regular episode.
Another visitor: Magnussen himself. He strolls in wearing (we think) his version of Google Glass with a blackmail app. It gives him pop-up reminders of his adversaries' pressure points. Mrs. Hudson's is "marijuana," which puts an entirely new twist on her perpetually chirpy blather. While Sherlock's are listed as "John Watson, Jim Moriarty, Irene Adler, The Hounds of the Bakerville and Redbeard."
Sherlock crafts a plan to break into Magnussen's impenetrable office to steal letters being used to blackmail Lady Smallwood. The only way into his office is for Magnussen's aide to give him access and we discover that person is, of course, Janine. When Sherlock pops out a ring to show her on the video camera suggesting he intends to propose -- a hugely lousy way to do it, by and by -- we're mortified for her.
Thankfully everything moves too fast to really think about how implausible it is that Sherlock's plan is to carry on a relationship with Janine when she merely guards the place Magnussen normally does not keep his blackmail materials on the off chance Sherlock will one day those know those materials will be there and that Magnussen will not be there so that he can try to break in. Sorry, but I have to call some of this stuff out.
Sherlock finds Magnussen held at gun point -- by Mary! We had a hint that Mary had a connection to "CAM" as the telegram in the wedding episode indicated. But we didn't expect her here. And we definitely did not expect her to shoot Sherlock in the chest.
What happens next is fantastic. Just fantastic. We go into Sherlock's mind palace as he scrambles to intellectually process his own shooting and how to survive it. There's really not a whole lot he can actually do, but he tries his best. We see Young Sherlock Holmes, with Mycroft berating him for being stupid. We see him with his dog -- so that's Redbeard! And we get the return of Moriarty representing death trying to drag him under. "You're going to love being dead, Sherlock. No one ever bothers you." But the thought of Mary endangering John brings him back. It's a bit like The 5 People You Meet in Your Memory Palace.
When he comes to in the hospital, we learn Janine sold stories of their affair as revenge to the tabloids ("Shag-A-Lot Holmes"!). Sherlock leaves the hospital, and it doesn't take John long to figure out what happened. Sherlock lures Mary into a confession in front of John. We learn she's a former intelligence agent who's done some bad things, changed her identity and is being blackmailed by Magnussen.
So here's the rundown of what happened, best I can tell: John and Mary's relationship was real and wasn't part of any scheme. Magnussen was targeting Mycroft, whose weak spot is Holmes, and Holmes weak spot is John, and John's weak spot is Mary -- thus he went after Mary to entrap the whole chain. Magnussen stuck Watson in the bonfire to test his theory. Okay? Okay.
NEXT: Why isn't Sherlock more popular?