Series I finale aired Sunday, November 7, on PBS.

Sherlock Holmes would be nothing without John Watson. It’s easy to forget that, what with all the attention-grabbing deductive shenanigans and outrageous displays of arrogance, but stalwart Watson is not only the frame by which the stories are told (the conceit of Arthur Conan Doyle’s fiction is that Watson is recounting his friend’s adventures); he also, more important, is practically the only story element that humanizes the iconic detective. Without Watson, Holmes would be unbearable and incomprehensible; even with Watson at his side, he’s a pill.

So Watson is key. He can’t just be a dumb loyal dog trotting after his master—that gets old fast—but there still has to be a reason that he puts up Holmes’s abuse. Holmes only has to make sense in relation to Watson, but Watson, as our portal into the story, has to make sense in himself.

What I love most about Sherlock, the BBC’s clever modern-day take on the detective (recently broadcast in the United States on PBS), is that it seems to understand that: the odd, prickly relationship between Holmes and Watson is central to the show and vividly dramatized. Watson might not be able to keep up with Holmes’s mental gymnastics, but he’s not a passive sounding board. He talks back, and he learns, and in his own way, he’s just as alienated from society as the great detective—an interesting, provocative take of the familiar Holmes-Watson dynamic. The show has its weaknesses in other areas, but with this pair at its center, it can’t help but be a smashing success.