In the episode, the alien time traveller known as the Doctor encounters River Song on the colony of Mendorax Dellora in 5343, with one of her husbands, Hydroflax (Greg Davies), who has an invaluable diamond lodged in his brain.

"The Husband of River Song" was met with generally positive reviews; critics particularly praised the chemistry between Capaldi and Kingston, but were unsure of the comedic tone of the episode.

In 5343, on the human colony of Mendorax Dellora, the Doctor is mistaken by a servant, Nardole, for a surgeon hired by River Song to attend to her dying husband, King Hydroflax, a cyborg.

River fails to recognise the Doctor and tells him to decapitate Hydroflax so she can claim the most valuable diamond in the universe, which has become lodged in the king's brain.

Showrunner Steven Moffat originally planned "The Husbands of River Song" to be his last episode for his run of Doctor Who,[1] but it became clear he would stay on because his successor, Chris Chibnall, was busy with the third season of Broadchurch.

[4] The episode fills in a part of River Song's timeline, the singing towers of Darillium, previously described in "Silence in the Library" and "Forest of the Dead".

[2] The episode makes multiple references to River's description of Darillium in "Silence in the Library" and "Forest of the Dead", such as the Doctor's new haircut, best suit, and tears.

[10][11] As for the villain of Hydroflax, Moffat commented, "I wanted to keep it simple, for Christmas: a big, bad, rather stupid man, who isn't much of a threat to anything because he's so thick".

[4] In September 2015, it was announced that Alex Kingston would reprise the role of recurring character River Song for the first time since the 2013 episode "The Name of the Doctor".

[15] Lucas was a fan of the show and Davies accepted the offer without reading the script, describing the role as "one of those jobs that validates the career to my own mother".

[16] Lucas shot the episode in between attending rehearsals for a BBC Cymru production of A Midsummer Night's Dream, where he played Nick Bottom.

[20] The street in which the TARDIS lands was a redressing of the set of "Face the Raven", and the company Snow Business provided winter effects.

[39] IGN gave the episode a score of 8.4 out of 10, describing it as "a nice, fun, wacky change of pace that still manages to touch that sweet spot of emotional resonance that the Twelfth Doctor has done so well this year".

[31] Paste Magazine's Mark Rozeman, giving the episode a score of 8.2 out of 10, noted that the lighter tone was welcome after the dark ending of series 9, but that it made "the hour feel a bit slight and lacking anything to really latch onto".

[33] He praised the episode as a "poignant swansong" to River Song that "sends her off in a blaze of glory, highlighting the fantastic energy and charm that Alex Kingston brought to the role".

[35][37] Mulkern wrote, "It's hard to pinpoint what is lacking from this episode but it feels as though, with an extra twist, funnier escapades and sharper banter for the duo, this could have been a classy screwball comedy".

[35] Setchfield found the setting "a little vague around the edges" and Lucas and Davies's characters also lacking depth, but he praised Capaldi's comedy and "cracking rapport and energy" with Kingston.

[48] Pieces of score from this episode, as composed by Murray Gold, comprise the entire fourth disc of the ninth series's four-CD soundtrack, which was released on 27 April 2018 by Silva Screen Records.