I’m generally a fan of Sherlock (the modern reimagining of Sherlock Holmes by Steven Moffatt and Mark Gatiss that’s so ubiquitous I’m just going to assume you know about it). I have some rather lengthy thoughts on how Moffat’s handling of Doctor Who has gone off the rails that I may spew across the Alexandrian at some point, but Sherlock has managed to mostly avoid those problems.

Mostly.

Unfortunately, there’s a real danger that the problems Sherlock is currently laboring under could turn into a metastatic cancer on the series (as evidenced by Doctor Who).

Let’s first consider the decision to simply not resolve the cliffhanger at the end of the second series. The ambiguity they attempted to embrace is arguably interesting, but it’s a burnt earth approach to writing: They presented a seemingly insoluble puzzle, implied that the solution to it would be amazing, and then deliberately failed to deliver. Fair enough. But that means the one thing that won’t be effective again is hanging a cliffhanger on a seemingly insoluble mystery: No one is going to take it seriously because you’ve already made it clear you have no intention of providing a satisfactory conclusion.

And yet what do they do literally three episodes later? Present the exact same cliffhanger a second time, but this time featuring a different character.

That would be lazy and uninspired writing at the best of times. But it’s particularly anemic because they’ve already established that they have no intention of following through.

Fool me once, shame on you. Fool me twice, I stop watching your show.

The more insidious problem, however, is the sloppy writing in the third series. (Exactly the sort of sloppy writing that we’ve been seeing a lot of over in Doctor Who.) A key example is the end of the season finale: It depends entirely on Magnussen failing to search them for weapons, despite the fact that the episode explicitly established that Magnussen has everyone he meets with searched for weapons. (It’s particularly silly because the only thing establishing Magnussen’s paranoia about weapons accomplishes is to render the ending of the episode into nonsense.)

In order for Sherlock to work as a series, it has to deliver sharp, clever scripts that support the conceit that its main character is sharp and clever. If it stops doing that it’s going to die a quick death, no matter how sexy and talented its two main stars may be.