By some accounts, 2016 has been… well, not great. It has also been a year without a new episode of Doctor Who. Coincidence? Yeah, probably. But before the year is brought to a close, the Doctor is here to bring a little Christmas cheer in the form of some brain-swapping aliens, Matt Lucas's Nardole, and Justin Chatwin as a Superman-esque superhero named The Ghost. And naturally, being the only new bit of timey-wimey Doctor-filled adventures delivered by the BBC (and BBC America for those of us on the other side of the pond) this year, there's a lot riding on the hour as both an annual holiday TV tradition and the series itself.

There is more to it than that, though. In a sense, 'The Return of Doctor Mysterio' is the beginning of the end. It's the second to last Doctor Who Christmas special exiting showrunner Steven Moffat will helm, making a holiday-themed bookend to his tenure with the Doctor. The episode also works to establish some of what will be coming along with the 12 new episodes in 2017. Front and center, is the aforementioned Nardole, who made a memorable appearance last Christmas, even though it meant losing his head. Nardole's head seems to be attached to the right body now, as this Christmas the cherubic oddity operates as the Doctor's interim companion of sorts while the series continues to move away from Jenna Coleman's Clara Oswald and prepares to welcome Pearl Mackie's Bill Potts.

The new season will reportedly also feature an expanded role for Lucas, who apparently wowed the folks in charge with his character to such a degree that Nardole will have a supporting role throughout season 10. That makes the Christmas special something between an actual Doctor Who one-off and an amouse-bouche for what's to come when the show is finally back on the air. As such, the dynamic between Peter Capaldi and Lucas is one to keep an eye on throughout the episode, as it may give some indication as to how the former plans to present his version of the Doctor next year. Capaldi's time as the Doctor has been marked in part by his unique take on the character, one that saw him more distant and, well, alien, and sometimes a little curmudgeonly – though considering what he's been through lately it's a surprise that he hasn't gone deeper into the ever-so-slightly detached characterization that has served Capaldi so well during his run.

Instead, after the events of season 9 – the sort of death of Clara and the Doctor's billion-year journey burrowing through a wall made of diamond – it seems that the latest iteration of the character has seen his two alien hearts grow three sizes. And the show has, too. Last Christmas, 'The Husbands of River Song' delivered a welcome heartfelt special, and 'The Return of Doctor Mysterio' follows suit, making for a Christmas special that mostly tries to make up for the time it has spent away from its audience.

The result, then, is an episode that feels more like an average installment of Doctor Who than a typical Christmas special. All of the key ingredients are present: the Doctor kicks things off with an in medias res opening, there's the threat of an alien invasion, and the aliens themselves have a weird, slightly cumbersome ability that helps them to stand out in the throng of extraterrestrial beings the Doctor has encountered over the years. This time, it's a group of brains – sort of like Krang from Teenage Mutant Ninja Turtles – surgically inserted into human bodies (or vehicles, as they refer to them). The use of a visual cue to tell who has had their brain swapped is a diagonal slash across the victim's face that also allows the head to open up – in one case revealing, of all things, a place to store a gun. While the use of the visual cue is striking, and the aliens' creepy surgeons signaling an unpleasant fate for the victim, the episode is never invested enough in the threat of invasion or who the aliens are to make the absurdity of their abilities rise above their rote plan to slip into the heads of the world's leaders.

Instead, 'The Return of Doctor Mysterio' is far more interested in exploring the relationship between the Doctor and Chatwin's Grant Gordon – who also happens to be the Ghost – and, Gordon's relationship with his ladylove Lucy Fletcher. The entire exercise is a mostly charming goof on the Superman mythos, but with the Doctor inadvertently granting Grant his superhuman powers as a child one Christmas Eve long ago. The result is a Three's Company-esque domestic comedy that sees Grant acting as nanny to Lucy's child, while also flying around the city saving people as a good superhero should.

Moffat has a good time playing with the idea of the role perception plays in maintaining a superhero's secret identity – especially one like Superman – making the comedy of Grant and Lucy's romance a cross between directly spoofing Superman: The Movie and paying homage to its earnestness. The regard for the Superman mythos is also present in a number of Easter eggs, like the reference to Jerry Siegel and Joe Shuster, that afford the episode a certain amount of leeway in terms of both its comic book aspirations and its gentle mocking of the character's concealment of his secret identity.

Chatwin and Wakefield make for charming proxies of Clark Kent and Lois Lane, even if Grant's interest in and devotion to Lucy borders on creepy at times, and the less said about his skills as a nanny the better. And charm can go a long way in a story that gets as muddled as 'The Return of Doctor Mysterio' does. The episode never manages to go all in on any of its threads, making each one feel like a missed opportunity for something grander. But no opportunity feels more squandered than that of the Doctor checking in on the boy he gave superpowers to at various stages in his life. There's a compelling story in the idea that Grant would have been mentored by his time-traveling benefactor during his development, and that the Doctor would have helped mold him into the hero he eventually became. Instead, the episode settles for one encounter to make a goof at how difficult having godlike powers would be while going through puberty. Instead of a deep dive into what makes a hero and the struggles that go along with growing up, Doctor Who settles for an obvious joke.

Unfortunately, 'The Return of Doctor Mysterio' is too intent on using Lucy and Grant's eventual romance to underline the Doctor's loss of River Song, which has to be spelled out by Nardole in the episode's closing moments. Using the arc of two characters to tacitly examine the series' protagonist is understandable, but it never quite matches up with the exuberant fun the show has with this playful superhero narrative.

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Doctor Who season 10 premieres in April 2017 on BBC America.

Photos: BBC