[2][3] It was written by Steven Moffat and directed by Nick Hurran with music composed by Michael Price and David Arnold.

The episode is a contemporary adaptation of Sir Arthur Conan Doyle's short story "The Adventure of Charles Augustus Milverton".

In the episode, Sherlock Holmes (Benedict Cumberbatch) and John Watson (Martin Freeman) take on a case about stolen letters.

This leads the pair into conflict with Charles Augustus Magnussen (Lars Mikkelsen), a media mogul specialising in blackmail whom Sherlock despises.

Moffat also won the Primetime Emmy Award for Outstanding Writing for a Miniseries, Movie or a Dramatic Special for his work on the episode.

John Watson, whose wife Mary is now visibly pregnant, finds an unkempt Sherlock Holmes in a crack house under the influence of drugs.

He deduces that she intentionally shot him in a non-lethal spot and, using a ruse, exposes Mary's secret life as an assassin to John.

The couple is spending Christmas with the Holmes brothers at their parents' home, where Sherlock takes the opportunity to drug everyone but John so that they can steal Mycroft's laptop.

Sherlock offers to trade Magnussen's information on Mary for the state secrets contained in Mycroft's laptop.

With visible joy, Magnussen reveals that the plan will not work because his vaults don't physically exist; the data are in his mind palace.

When Mycroft and the police arrive, Sherlock coldly shoots Magnussen in the head, realising that this is the only way to free his friends and everyone else from his power.

Mycroft convinces the government to spare Sherlock a trial and, as an alternative punishment, press him into a high-risk mission in Eastern Europe.

However, he is recalled within minutes when video screens all over Great Britain begin to broadcast a loop of a static image of Jim Moriarty asking "Did you miss me?"

In both stories, "Appledore" is the name of the antagonist's vaults, and in both, Holmes becomes engaged to an employee of the villain to gain access.

In The Sign of Four, the first original Holmes story to feature Mary Morstan, the Agra Treasure is a main focal point and cause of dispute.

[9] According to Gatiss, Mycroft's line, "As my colleague is fond of remarking, this country sometimes needs a blunt instrument" is a reference to a comment by M describing James Bond, and is intended to suggest that the two series share the same reality.

[10] In July 2013, it was announced that Danish actor Lars Mikkelsen would star as the main villain of the third series of Sherlock.

[12] Mikkelsen was suggested for the role by producer Sue Vertue and recorded an audition video for the production team in which he urinated in his barn.

[15] However, he joked that he was as surprised as the viewers to see Moriarty return, noting that it is impossible to fake shooting oneself in the head.

"[20] Director Nick Hurran had previously worked with Steven Moffat on several episodes of Doctor Who, including the fiftieth anniversary special.

[30] The British Board of Film Classification gave the episode a 12 certificate, for "moderate violence, drug references and one use of strong language".

[33][32] "His Last Vow" received critical acclaim, with Louisa Mellor of Den of Geek saying that the episode was "as good a finale as Sherlock's ever had", with a very strong plot.

[41] However, Neela Debnath, also of The Independent, said that the episode was "trying far too hard and is coming across a tad foolish", and consequently "failed to hit new heights".

[43] The episode deviated from source material by removing the woman who, in Doyle's story, had shot Milverton (Magnussen in the adaptation) [44] After the airing of "His Last Vow", Moffat and Gatiss said in an interview with Empire Cinemas: Moffat: Also, if you read [The Adventure of] Charles Augustus Milverton, Dr. Watson in the opening paragraph tells you that he's about to tell you a porkie.

I think what Doyle is hinting at is that Sherlock Holmes and Dr. Watson sat in Baker Street and said, 'Right, we're going to have to go and kill him, aren't we?

[44] Steven Moffat's writing, said Emma Dibdin of Digital Spy, is "a few degrees colder than his colleagues'", which helped the episode go back to the "cerebral, mystery-driven tone some viewers have been left craving".