It has been quite a while since Elementary tackled issues pertaining to Sherlock’s sobriety. At the end of last season, he was in possession of a small amount of heroin. The question, naturally, was whether or not he would be able to resist the temptation of using again. This was during a rather tumultuous time when Sherlock and Watson were on the outs, and with everything that had happened regarding Mycroft, it seemed inevitable that Holmes would fall into an old, dangerous routine. Despite the destruction he did cause, Sherlock managed to stay clean. But that was the long and short of it. Aside from Sherlock’s assurance he didn’t use, the character’s ongoing sobriety has been hardly discussed in the seven episodes that have transpired this season.

In a sense, Sherlock’s sobriety is like its own recurring guest star: It’s always within reach, when the story calls for it. But like any recurring thread or character, its involvement must have some sort of significance with the larger story at hand; otherwise, it’s just a wasted opportunity. Here, it’s not so much a question of whether or not Sherlock is going to use again – even though it is a major component of Elementary‘s narrative, that particular threat is one that needs to be used sparingly.

Instead, the issue in ‘End of Watch’ concerns a fellow recovering addict turning Sherlock’s in-meeting observations and discussions into a website filled with daily affirmations. Although the intent of the website is sound – after all, even Kitty mentions how quotable Sherlock is – the effect the sudden lack of anonymity has on the detective becomes a serious impediment to his work and, as the episode suggests, his continued participation in meetings.

This would be a compelling enough plotline for any episode of Elementary, but ‘End of Watch’ manages to use Sherlock’s distraction as a tool to raise the stakes of the procedural storyline concerning a cop killing gun dealer named Niko Buros (Robert Mammana). The episode begins with Sherlock speaking about “the dull routine of existence,” which is contrasted with the death of officer Flynn. The two plot elements are woven into the overall narrative so well they almost become one thread. Generally, there’s a slight disconnect between the main procedural plot and the more character driven needs of the B plot. But here, as it concerns Sherlock’s ongoing distraction with the BrainAttic website, the B plot manages to have a direct effect on the investigation into Flynn’s murder.

Naturally, this means that the episode strikes a much darker and more serious tone than last week’s far more lighthearted ‘The Adventures of the Nutmeg Concoction‘ – which is weird considering it, too, revolved around a nasty string of homicides. But rather than seem inconsistent, it demonstrates how, despite playing in the same procedural sandbox week in and week out, Elementary has a striking number of storytelling tools at its disposal. In fact, the shift in tone accentuates the question that’s at the heart of the story: Must Sherlock strike a balance between the needs of his sobriety and the needs of the people his words (and actions) may help? After Sherlock unsuccessfully confronts Daren (Gregory Abbey) about BrainAttic, he’s forced to resort to a scare tactic, quickly deducing the quote collector to be a collector of relationships outside his marriage as well, and threatening to expose him if the page isn’t taken down.

What’s striking about the episode, then, is how it plainly demonstrates the way Sherlock’s distracted state leaves him unable to notice two essential clues that eventually lead the NYPD to Niko, while simultaneously clearing the name of one of the cops he killed. And while the investigation uncovers a dirty cop, and successfully recovers the guns stolen from a weapons depot, ‘End of Watch’ once again plays with uncertainty in a compelling way.

Just as it did in ‘Bella‘ – though it’s not as overt or creepy – the episode leaves viewers to contemplate Sherlock’s thoughts. This time, though, it’s his reluctance to share those thoughts during a meeting that has the greatest impact. By not offering an answer to Sherlock’s quandary, or offering any explicit insight into what he’s thinking, the episode succeeds in delivering a poignant observation of the character’s constant inner struggle by adding another layer of complication to it. This time, the struggle isn’t just between a man and his addictions, but between a man and how he balances the moral obligation to himself with the obligation to help others.

If nothing else, this is an interesting test of Sherlock’s limits, and for an episode that was primarily devoted to an exploration of his character, ‘End of Watch’ offered some compelling observations.

Elementary will return after the holidays on CBS.