I thought this episode was certainly entertaining… but also had a few teeth-grittingly implausible moments:
(1) a guy was killed by being hit on the head by a boomerang? Uh-huh… the kind of boomerangs that actually come back are just not very heavy.
(2) as others have pointed out, the twist ending with Sherlock infiltrating the terror cell is just a scene from a different show entirely (not to mention that whatever ungodly place they were in apparently had cell reception compatible with Sherlock’s British cell phone)
(3) the main airplane plot makes less sense the more you think about it. So, I guess the sequence of events is this:
(a) There’s a group of terrorists planning to bomb flight 007
(b) MI5 (or whoever) has infiltrated them
© MI5 learns about this plot
(d) MI5 comes up with the plan of launching a plane full of corpses so the terrorists can go ahead with their plan and think they succeeded, not realizing they have been infiltrated
(e) Some MI5 guy brags to Irene about this, in vague terms, she takes a picture of an email he has
(f) She doesn’t know what this email is or what’s in it, so she calls up Jim Moriarty and says “hey, I have some potentially valuable info”, and he is so excited that he abandons his kill-Sherlock-Holmes-by-the-pool plan and dashes off
(g) He organizes things so that Sherlock Holmes meets her, knowing that Sherlock will instantly crack the code
(h) Sherlock cracks the code
(i) Irene calls Moriarty back, tells him that it’s seats on a jumbo jet
(j) Moriarty then immediately grasps the overall plot
(k) Moriarty does something that ruins the plot and profits from it
(l) Moriarty calls up Mycroft to taunt him about it
OK, aside from the preposterous overcomplexity of it, here are some implausibilities, right off the top of my head:
(d) is superficially clever, but makes less sense the more you think about it. The corpses really add nothing, it’s not like there are going to be photos of the wreckage on the ocean floor published. And of course there’s the issue of the lack of grieving families that someone is going to twig onto. Not to mention that the airline will have to be in on the secret
(f) is also questionable… Irene is obviously a smart cookie. But she seems to make a good living in the dominatrix business. If she just hangs onto this photo to use as leverage in some hypothetical future when she needs leverage, then she can continue her happy and safe life indefinitely. Instead she takes an action that is pretty much guaranteed to bring her to the attention of lots of people who will want to kill her. And it’s also unclear why Moriarty would so instantly find “I have some information that’s in code that a guy from the government bragged was important” so instantly fascinating.
(g) Doesn’t make much sense… Moriarty is also a genius. If Sherlock can crack the “code” in under a minute, Moriarty could presumably do so in a few hours. (Not to mention, of course, that this all depends on it not being a “code” at all. Nothing we’ve seen leads us to believe that Sherlock could break actual cryptographic codes in under a minute, or ever.)
(i) How does knowing that it’s seats on a jumbo jet let Moriarty deduce the full scope of the plan?
(k) How does Moriarty know who to contact in order to profit, and what to tell them? How would that transaction work?
(l) And assuming Moriarty is profiting by telling the bad guys they’ve been infiltrated, then he turns right around and screws them over by telling MI5 that they know. Obviously it’s way way more valuable to the baddies if they know they’ve been infiltrated by MI5 doesn’t know they know.
(I suppose that (l) isn’t an issue of Moriarty is just trying to cause chaos, not actually make money, but have we seen any sign of that?)
Oh, and while we’re at it, the whole sniper standoff by the pool last season made no sense either, but that’s a different topic.
Thus, the bombing has to go off (pun intended) as scheduled. Maybe the ruse only had to “work” for a short time, before the human-interest-profile phase of news coverage would kick in.