We sorely needed a light-hearted runaround after the heavy drama of the recent series of Doctor Who, and this certainly delivered that. It's hard to call this anything particularly remarkable for Doctor Who. It's hard to make a Christmas special feel special when it's only been about three weeks since the last series finished; Doctor Who is very concentrated into the last few weeks of the year now, which does suit the spooky direction we've gone in lately, but does reduce its overall impact on the screens.
In any case, this was good fun, if nothing spectacular. A ludicrously over-the-top sci-fi story with more than a hint of Hitchhikers to it, with the broad comedy set-up used as a background for River and the Doctor to play together. The conceit of bringing River back, yet again, but pitting against a Doctor without the boyish looks of her previous Time Lord boyfriends is a good one, and having River unaware that this is the Doctor at all is a great idea. As the Doctor says, it's a chance to see what River is like the rest of the time, having her own adventures, playing up how flirtatious, amoral and downright dangerous she is. The script flirts with the idea that River is just using the Doctor as a handy ride in times of trouble, but swivels and has her declare her love for him in an astounding speech. Either way, she is revealed to be enormously dependent on him, even as she lives a long and elaborate life of her own.
It has to be said, Greg Davies and Matt Lucas, although both pretty funny here, are wasted in the roles of Hydroflax and Nardole (a particularly unfortunate little character, he really gets put through the ringer). As is Game of Thrones's Nonso Anozie, who provides the booming voice of the robotic body that carts the various characters' heads around. It's really a showcase for Capaldi and Kingston, who play things mostly straight while the farce carries on around them, displaying admirable comedic skills and great chemistry with one another.
Both of the main settings for the episode have potential, but neither is explored in any kind of detail. This is a pity; the horrific reign of King Hydroflax could have been a mine of material, but perhaps Hydroflax is just too straightforward a villain for modern Doctor Who, suitable only as a vague threat and comic relief. Another potential source of villainy and adventure is the starship Harmony and Redemption, the misnomered cruise liner for the worst scoundrels and despots in the Galaxy (having committed genocide in the past, the Doctor would have no trouble booking a cabin). A shipful of supervillains could provide a series' worth of material, but it's little more than a throwaway gag here. There's a lot more that could have been done with this setting.
What made the episode for me was the ending, beginning with River's impassioned speech (and the Doctor's merciless teasing of her for it), and moving into their, we presume, final adventure together. Bringing back material Moffat wrote for River when he first created the character, it puts a different perspective on the Doctor. The man who doesn't like endings - who refused to even countenance the idea of Clara dying - finally has the courage to accept this is the beginning of the end for them. Having put off the fateful trip to Darillium for so long, he and River share what seemed to be their final moments together in front of the Singing Towers. It's utterly beautiful, shows Capaldi and Kingston at their absolute best, and ends with a doozy: they've actually got twenty-four years to spend together in their one, final night. Although the comedy nonsense was fun, this is where the strengths of both performers and the writer lie.
From River's perspective, this episode takes place shortly after the events of The Angels Take Manhattan, a little time after the mini-episode "Last Night" and immediately before she leaves for the Library, in The Silence of the Library/The Forest of the Dead (allowing for twenty-four years at Darillium). Other adventures referred to in her diary include The Pandorica Opens and the crash of the Byzantium in The Time of Angels. Back in 2008, in The Forest of the Dead, River told the story of how the Doctor turned up, "with a new haircut and suit," and how "the Towers sang, and you cried, and you wouldn't tell me why." The Doctor also gives River his screwdriver, which will e very important in said episode.
As suspected, River has an augmented lifespan as part of her Time Lord-esque physiology, and is two hundred years old. This episode is set in the 55th century, and she refers to digging up the crashed ship's remains four hundred years later. Most adventures have put River as a 51st/52nd century resident, but then, she does time travel an awful lot. As previously suggested, River has a spotter's guide to all the Doctor's incarnations, or at the very least, all those from his first run of regenerations. She's clearly aware that Tennant counts as two lives, and she even has a picture of the War Doctor.
River may in fact be naked throughout this episode, if those are in fact holographic clothes she's wearing. The Doctor's antlers are certainly holographic, although he uses the fluff-term "hologrammatic," which was popular on Red Dwarf.
Both the Doctor and River admit to having multiple spouses (of varying legitimacy), including at least two wives for River. The Doctor has been married to Cleopatra (who we previously only knew he was involved with somehow), Elizabeth I and Marilyn Monroe, while River is here married to both King Hydroflax and Ramon, and has apparently married Stephen Fry. I'd have loved it if they'd had the guts to go all out and call them polyamorous.
Quibbling: The starship Harmony and Redemption is said to be reaching the fourth galaxy on its tour, the Andromeda Galaxy, but immediately afterwards it is stated to approaching Gamma Eridani, which is a mere 150 light years away in our own galaxy.
Best Line: "Are you thinking? Stop it, you're a man - it looks weird!"