Doctor Who - The Husbands of River Song, on BBC One (UK) / BBC America (USA)
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Caution: spoilers.

This is the eleventh Christmas special of the revived Doctor Who series. It aired on Christmas in 2015, but I didn't see it until September 2018. It's unclear exactly how much time has passed for the Doctor since the end of series 9, but I suppose that's not of immediate importance. He shows up on some human colony world on Christmas Day in 5343, where a man named Nardole is looking for a surgeon who has been summoned by his employer. He mistakes the Doctor for the surgeon, and the Doctor goes along with it. When Nardole takes him to his employer, it turns out to be River Song. The Doctor is happy to see her, but she seems not to know him. At first I thought this might have been before she ever met him, though upon reflection that's impossible. I mean, certainly it's the first time she's met this version of the Doctor, but we already know when the first time she met him was. I think. That just didn't really occur to me while I was watching the special, because I'm used to their respective timelines being so mixed up.

Anyway, she had summoned a surgeon to operate on her husband, a tyrant named King Hydroflax. When she takes the "surgeon" aside to explain things to him, it turns out she doesn't really want him to save her husband's life, but rather to extract a priceless diamond from his head. And the easiest way to do that would simply be to remove his head. But... his head is actually attached to a robot body, and it turns out to be easily removable. In fact, when Hyrdoflax discovers what River is planning, he removes his head himself. Which... was probably not great thinking on his part, because River and the Doctor manage to grab the head, stuff it in a bag, and teleport away. It's then that the Doctor meets another husband of River's, her partner in crime, Ramone. River and the Doctor get to the TARDIS, but it can't take off, at first, for a reason I won't get into. But before long it does take off, and goes to a spaceship where River plans to sell the diamond. But Hyrdoflax's robotic body comes along for the ride, and... I don't want to give too much away about that, but it causes a lot of trouble. And throughout everything, the Doctor keeps trying to drop hints to River about who he is. It's all terribly amusing, despite the fact that River seems far more oblivious than I would expect her to be. But that is explained by the fact that she still thinks the Doctor could only have thirteen lives, and she knows what all of them look like. I suppose, then, that it makes sense it would never enter her mind that someone she's never seen, even in a picture, could possibly be her Doctor. (It's also quite possible that her emotional grief in regard to him played a part in clouding her observational skills.) But when finally she does realize who he is... she immediately shifts gears and becomes the same old River, working in perfect harmony with the Doctor.

Beyond that, I don't want to reveal anything in particular about the plot. But I will say that the special is full of lots of great humor, and some very dramatic moments, and a pretty nice date at the end (which the Doctor does a good job of setting up, via time travel). And the special ties in nicely to some of their past/future encounters (depending on your temporal frame of reference). And... I dunno, it was all just a lot of fun (as no encounter with River could possibly fail to be).