It was written by co-creator Mark Gatiss, who also portrays Mycroft Holmes, Sherlock's brother in the series, and was directed by Paul McGuigan.

In the episode, Sherlock (Benedict Cumberbatch) and his crime-solving partner John Watson (Martin Freeman) take on the case of Henry Knight (Russell Tovey), who 20 years earlier witnessed the brutal killing of his father by a "gigantic hound" on Dartmoor.

As opposed to traditional ghost stories, Gatiss's plot focused on more contemporary horrors, conspiracy theories and genetic modification.

Sherlock and John receive a visit from Henry Knight, who witnessed his father's being killed by a "gigantic hound" on Dartmoor 20 years ago.

Searching the lower levels of the genetics labs alone, John finds himself trapped and then hears growling, which he assumes is the hound.

As Henry calms down, they all fall under the influence of the gas and see a savage dog preparing to attack them, and John shoots it.

[5] Tovey, who liked Sherlock for staying true to the style of the novels despite its modern twist, said of the experience: "It's amazing to be a part of it", adding, "I got to act with Benedict and Martin which was awesome".

[7][8] Conan Doyle had killed off his famous character in the 1893 story "The Final Problem", but bowed to popular pressure to write another Holmes adventure.

Gatiss observed that Conan Doyle's weariness with the character is demonstrated by Holmes' absence for half of The Hound of the Baskervilles, in which Doctor Watson's role is foregrounded.

Also, Gatiss suggested the concept of a "mind palace", a memory technique originating in Ancient Greece; the idea came from a book by illusionist Derren Brown.

Writers also posited that Henry's father's murder involved revenge after he had an affair, but the producers and Gatiss found it easier to mention he died because he learned of Frankland's experiments with the hallucinogenic gas.

The ending also changed; the final scene had originally involved Moriarty entering the Tower of London but that was held back for the following episode.

[2] Throughout his scenes, Rupert Graves was tanned because before filming the episode, the actor was in Guadeloupe, an island on the Caribbean, appearing in Death in Paradise.

However, after visiting such a locker in Bristol, the producers came to realise that it would be too expensive, and cold for Freeman, forcing them to change the setting to the Baskerville labs.

"[21] The episode, which is accompanied by an audio commentary by Moffat, Gatiss, Tovey and Vertue,[22] was released with the remainder of the second series in the UK on DVD and Blu-ray on 23 January 2012.

In a pre-broadcast review, Terry Ramsey of The Daily Telegraph labelled the story's shift from a Gothic house to a military research base "an inspired piece of modernisation".

[28] The Radio Times's David Butcher compared the episode to Steven Moffat's series opener, "A Scandal in Belgravia", saying this "is more of a creepy affair, all jittery camerawork, paranoia and suspense.

"[29] Christopher Hootan of Metro thought the episode was "the perfect marriage of misty, moor-based foreboding and modern, fast-paced thriller," adding that "with a breakneck script and captivating acting from Benedict Cumberbatch, Sherlock offers about the fastest hour and a half of television going at the moment.

With adroit plotting, sneaky inversions, excellent grounding in source and genre, and a delicious sense of mischief comes Gatiss' answer in the form of The Hounds of Baskerville.

Episode 2.2 serves up a psychological horror that gives good scare before revealing its supernatural hound to have a very real-world provenance."

Louisa Mellor of Den of Geek believed the episode was "well-schooled" in the horror genre, "with plenty of freaking out and jumping at shadows.

Arnold and Price's elegant music came to the fore wonderfully in the largely wordless scenes of Watson and Henry's fearful hallucinations."

Mellor was also appreciative of McGuigan's "stylish hand" as director, particularly highlighting the "mind palace" sequence, as well as Tovey's performance as Henry Knight and for "once again" seeing Watson's role for being "more than just sigh exasperatedly at his flatmate and apologise to others on Sherlock's behalf."

"[31] Chris Tilly of IGN rated the episode a "good" 7 out of 10, but stated that although it was "full of mystery and intrigue," the central story "wasn't strong enough to fill the 90-minute run-time, running out of steam at the mid-way point and padded out with irrelevant and at times exasperating efforts to throw the audience off the scent."

Tilly praised Cumberbatch's performance as a mentally broke down Holmes, and Freeman for being "let off the leash this week, with Watson investigating solo on a couple of occasions," and also thought Tovey was a "fine addition to the ensemble.

"[32] David Lewis of CultBox called it "a pretty straightforward thriller about chemical warfare, cover-ups and a colossal canine.

[33] Morgan Jeffery of Digital Spy thought "The Hounds of Baskerville" was "an excellent installment of Sherlock — fun, moody and, at times, genuinely scary."

Jeffery felt that the final realisation of the hound was impressive, and praised the CGI work, as well as the performance of Cumberbatch and Freeman.

"[35] The Guardian writer Stuart Heritage stated; "Last night's Hounds of Baskervilles wasn't quite as rapturously received as other adventures, perhaps because of the amount of time that Cumberbatch and Freeman spent apart.

"[36] Jim Shelley of the Daily Mirror stated that the episode was "a disappointment," contrasting it against the original book as "a tedious treatise against vivisection."