Like all good science fiction, Doctor Who delves into commentary on the past and present of our culture from time to time. Given the series' emphasis on time travel, it is particularly well suited to deliver stories that can cut at humankind's history as well as its future, and that's a lot of room to run around and play in. In other words, no topic is too big or too small for the Doctor and his companion to tackle in some round about way or another. But unlike, say, Black Mirror, another British series intent on having its say about the way the people of Earth conduct themselves – especially when it comes to technology and communication, and the way the former seems to influence and change the latter in sometimes startlingly rapid fashion – Doctor Who can't be so blunt in its finger wagging. It is after all something of an institution telling more or less a single narrative rather than a satiric anthology series looking to turn your cell phone into the ultimate boogey man.
So when the series teases an episode like 'Smile', one that sees the Doctor and his new companion Bill encounter a group of semi-sentient emoji robots on the first planet colonized by humans, there's a question or two about what, exactly, Doctor Who is getting on about. Being the second of the tenth season, the episode has the freedom to play around with the core concepts of a single narrative more, which is actually a good thing, considering Bill is still incredibly new to all this timey wimey stuff, and although Pearl Mackie and Peter Capaldi demonstrated a really great and charming kind of chemistry during last week's premiere, the companionship needs to undergo a little more field testing before a real overarching plotline can begin to take shape.
In that sense, 'Smile' is the perfect way to explore the two characters' burgeoning relationship, by placing Bill's wide-eyed wonder front and center with a fittingly dark discovery about humankind's first colony being undone by some robots that communicate solely through, you guessed it, emoji. It's not hard to guess exactly what Doctor Who is getting at with the robots and their preferred form of communication, and, of course, the destruction of a large group of humans, and the episode isn't exactly subtle with regard to it intentions, either. Then again, Doctor Who doesn't have to be subtle, and there's reason enough to argue that it's better off being upfront about its intentions, especially when something like the Doctor's relationship with Bill is concerned and the season as a whole is marching toward the inevitable regeneration of the Time Lord at its end.
Where 'Smile' surprises, though, is in its structure. What at first appears to be a typically, and perhaps even refreshingly straightforward episode of Doctor Who soon exhibits telltale signs of outgoing showrunner Steven Moffat's writing. There are multiple threads running just below the surface of what is essentially a classic episode of Who: i.e., the Doctor and his companion travel to a distant place in space and time to find (thanks to the magic of budgetary constraints) a planet that should be teeming with life, but is instead almost entirely absent of it. The eerie mystery is the cornerstone of these kinds of Doctor Who episodes. The threat of a seemingly malevolent force lurking in the margins of the story gives episodes like these their ability to suck the viewer in, and 'Smile' is no different in that regard.
Where the hour surprises, though, is in how it uses a familiar Doctor Who structure as a delivery device for both the mystery at hand and a completely unrelated mystery that nevertheless hints at the season's bigger, overarching plot that will likely lead to the Doctor's regeneration. Before 'Smile' gets to its missing colonists and silly little killer robots story, the hour drops a rather large hint about the vault introduced in the premiere and the continued appearance of Matt Lucas's Nardole – who the Doctor not-so-lovingly dubs 'Mom.' It seems Nardole is there to ensure the Doctor keeps his oath – to stay on planet guarding the vault and its contents – and to make sure nothing happens with whatever's inside.
Sowing the seeds of a larger mystery before letting it sit to delve into a more episodic plot that still twists in on itself, moves toward a reliable deus ex machina, and then ends with another surprise is a great way to sum up the Moffat era of the series. But it also makes 'Smile' a more interesting early entry to the season than it might have first appeared to be. The basic plot beats of the killer emoji bots leads to some interesting character moments for both Bill and the Doctor. Capaldi continues to do great work as a Time Lord who cares deeply about others but only grudgingly lets those emotions bubble to the surface. And in her second outing, Mackie demonstrates an ability to balance the wide-eyed wonder she brought to last week's premiere with some genuine pathos that balances her exuberant curiosity about the Doctor and all the fascinating sites and people (or not people) she has so far encountered with very human moments of concern and compassion.
As the story about the colonists unfolds to reveal that they didn't all die off, but rather were mostly kept in a cryogenic state, Mackie show's an impressive range of emotion reacting first to the belief the human race has been wiped out and then the discovery that humankind has gotten a second chance. Mackie's acting choices offer the series the sort of breadth of emotional responses necessary to not only justify Capaldi's cooler, more aggressive Doctor, but to make the juxtaposition of the two time travelers interesting as much for how different they are as for how well they work with one another.
In all, 'Smile' turns what would otherwise have been a run-of-the-mill Doctor Who episode into a positive road test for the Mackie's companion and a gateway to a much larger story.
Doctor Who continues next Saturday with 'Thin Ice' @9pm on BBC America.