A bored Sherlock decides to take on the case of Henry Knight, who claims to have seen the footprint of a gigantic hound in the woods. He also claims that 20 years before he had seen his father mauled to death by the creature. Holmes assumes that the source of the creature is the nearby Baskerville military research facility. Using his brother Mycroft's identity card, he and Watson gain access to the facility though his ruse is quickly found out. His faith in his abilities is shaken to the core when he too sees the creature, something that genuinely frightens him.
The 21st century take on possibly the most famous work in the Holmes canon — The Hound of the Baskervilles.
- Adaptational Villainy: Frankland wasn't the bad guy in the original story. He was at most a crabby, litigious old man.
- Faux Affably Evil: Dr Frankland is very polite and friendly despite being a murderer involved in highly unethical scientific experiments.
- Animal Motifs: Due to Henry's PTSD from the attack, he is associated with dogs/hounds which foreshadows the hound's appearance and his resulting cynophobia.
- Arc Words: "Liberty" and "In", not to mention the eponymous hound.
- Badass Boast:Dr Frankland: I'd love to tell you, but then of course I'd have to kill you.
Sherlock: That would be tremendously ambitious of you.
- Artistic Licence – Military: British Army personnel are not allowed to have beardsnote However, Major Barrymore's full beard is a nod to the original canon character on which he's based, John Barrymore, who is described in the book multiple times as being a "black-bearded man."
- Bavarian Fire Drill: Sherlock and John manage to use two consecutively. They sneak their way onto the Baskerville base and have a look around. First Sherlock pretends to be Mycroft to get them onto the base with an ID he "acquired" long before, just in case; then John uses his ID showing his rank of Captain to get "the full tour" from the corporal who challenges their being there.
- Beard of Evil: Subverted with the Major.
- Beeping Computers: The computer at the facility, when they are hacking into the H.O.U.N.D. database.
- Black Site: The Baskerville facility is a highly secured military research centre. Sherlock and John manage to get inside by using Mycroft's ID and Bavarian Fire Drill tactics.
- Brief Accent Imitation: Sherlock briefly dons a Doncaster accent.
- Busman's Holiday: Lestrade is sent down by Mycroft to check on Sherlock, but also is on holiday. He gets roped into the case. John addresses him as "Greg", much to Sherlock's confusion.
- Casting Gag: Russell Tovey plays a nervous man haunted by wolves.
- Celebrity Paradox: Henry watches the 1959 film version of The Hound of the Baskervilles briefly on television.
- Chekhov's Gun:
- They mention a minefield at the beginning of the episode. It's not a matter of if someone gets blown up, it's when.
- A seemingly random e-mail Sherlock gets from a little girl asking to find her missing pet rabbit.
- The vegetarian pub owners ordering from a butcher. John finds the receipt in the first ten minutes; it's not important till the second act.
- Dr. Frankland says "cell phone" instead of "mobile" when he gives his number to Sherlock and John. Both this and the number itself (though we don't find out the number) become important towards the end.
- Chewing the Scenery: John, unsurprisingly, does this in the lab when Sherlock finds him, with John having thought the hound was trapped in there with him.Sherlock: It's all right. It's OK now.
John: NO, IT'S NOT! IT'S NOT OK! I saw it, I was wrong!
- Complexity Addiction: It turns out Sherlock lost a game of Cluedo because he simply refused to accept the idea Mr. Black was murdered and insists it had to be suicide as "the only logical explanation" ignoring that his being murdered is the entire point of the game.
- Continuity Nod:
- Before they're about to go into Baskerville for a second time, Sherlock tells John he'll have to go look for the hound on his own and says, "Could be dangerous". These are the same words he texted to John to get him to agree to help in "A Study In Pink".
- When John corrects Sherlock over his bad 'timing' in gloating over the case in front of his emotionally devastated client, Sherlock responds, "Not good?" This harks back to the first episode, in which Sherlock asked John the same question to understand that he had just said something that most normal human beings would consider too insensitive.
- Cryptid Episode: The episode centres around a mysterious "hound" that apparently killed the client's father in his childhood, near the Baskerville military installation. Sherlock and John chase this strange creature for the majority of the episode until it's realized they were suffering under the effects of a powerful hallucinogenic vapor that was being disseminated in a nearby wooded area.
- Dead Artists Are Better: Invoked by Sherlock when asked "why didn't they kill me?": "Dead men get listened to. They needed to completely discredit you."
- Dramatic Chase Opening: The opening scene of a boy seemingly running from a threat.
- Elaborate Underground Base: The Baskerville facility.
- Everyone Knows Morse: Justified in case of John, as he could have been trained in it in the Army. However, it turns out to be a Red Herring, as the flashes were caused by a guy's belt being caught on the switch in his car, as he's having sex with a girl.
- Exact Words: "What I said before, John, I meant it. I don't have friends. I've just got one." Somewhat blends with Poor Communication Kills.
- Although it's not really pointed at all when John appears beside the swimming pool in an explosive vest he was forced to wear by Moriarty, he seems to be blinking SOS.
- Filler: This is the only episode in the first two seasons with absolutely no connection to Moriarty and his machinations, and the only one to take place largely outside of London.
- First-Name Basis: An odd example with good old Maggie.
- Foreshadowing: John tells Sherlock that it's not possible for the victim to have committed the murder in Cluedo. This is more-or-less what happens in the next episode.
- Also, Sherlock's Complexity Addiction that a straightforward murder in a board game must be something more elaborate shows how in the next episode he easily fell for Moriarty's fake "super hacking bug"
- Freudian Couch: Henry Knight has a conversation with his therapist, Doctor Mortimer, about his recurring dreams, while lying on a couch in his home while she takes notes.
- Gaslighting: Frankland has been drugging Henry in order to discredit him as a witness to his father's death.
- Gender Flip: Dr Louise Mortimer. Corporal Lyons. Possibly Dr Stapleton depending on whether you think she's based on Jack or Beryl from the original (she doesn't quite fit either).
- Going Cold Turkey: The reason for Sherlock's manic behaviour during the Cold Open.
- Hate Plague: According to the CIA report found by Sherlock online, the hallucinogenic drug researched on at the Baskerville facility drove the test subjects insane and made them almost uncontrollably aggressive.
- Heroic BSoD: Sherlock is badly shaken by his encounter with the "hound", almost to the point of tears. He later realises that his out-of-character reaction was partly due to being drugged.
- Hoist by His Own Petard: In the climax of "The Hounds Of Baskerville", Frankland attempts to escape through the Grimpen Minefield and steps on a mine, which blows him to bits.
- Hollywood Spelling: Henry Knight tells Sherlock and John that he remembers "Liberty" and "In", without spelling out the latter. Averted earlier, when he does spell it out to his therapist.
- Played with. While Henry doesn't spell it for Sherlock, Sherlock quickly remarks the saying "Liberty In Death"; when he enters his mental Wiki-Walk, his mind does go to "Liberty Inn" as a possibility but can't make any meaningful connections and thus discards it.
- I'd Tell You, but Then I'd Have to Kill You: Said as a joke by Frankland when Sherlock asks what he does at Baskerville. It's more complicated than it looks at first, though: by the end of the episode, we learn that he has in fact personally killed at least one person who found out what he was doing.
- Insistent Terminology: One of the reasons Sherlock takes the case is that Henry refers to the thing that attacked his father as a "hound". It is a hound. Of sorts. Sherlock also refers to it as a hound, but John sticks to calling it a dog until the night he reports the sight. "It was the hound!"
- Karma Houdini Warranty: Double-subverted. Frankland was ultimately responsible for the death of Henry's father, and got away with it because even though Henry witnessed it, he was drugged by the Project Hound drug and rationalized it into thinking it was the hound to cope with the trauma. When Henry finally learns and accepts the truth about the hound and his father's murder near the end of this episode, twenty years later, he furiously tries to attack Frankland before being stopped by Lestrade. Frankland then attempts to escape through the Grimpen Minefield and, predictably, ends up getting blown up.
- Land Mine Goes "Click!": Dr Frankland dies this way, having unwisely decided to enter the Grimpen Minefield while trying to escape.
- Large Ham: Henry, especially when he sees the hound or thinks he does, or then, when he finally learns the truth, he tries to attack Frankland.
- Literal Metaphor: After Sherlock gains entrance to a secret military facility by using Mycroft's stolen ID, Watson observes that Mycroft's name "literally opens doors".
- Mad Scientist: Frankland killed a colleague who threatened to expose his unethical experiments, then spent decades psychologically tormenting the only witness, to guarantee that witness could never plausibly explain what he'd seen.
- My God, What Have I Done?: Henry, after shooting at his therapist.
- Mythology Gag:
- "Mr Holmes, they were the footprints of a gigantic hound!" is one of the most famous lines from the original novel.
- Sherlock's waffling about whether he will go to Dartmoor or send John to investigate is a wink at the fact that, in the Conan Doyle version, Holmes does send Watson down to Baskerville Hall in his place. Sort of.
- Major Barrymore sports a thick dark beard, in spite of the fact that it's usually against army regulationsnote . This is because the original character's most distinguishing physical characteristic was a black beard.
- In the original novel, the lights in the moor at night lead Watson to the escaped convict Selden. In this case, a Mr. Selden is the cause of the flashing lights, but not quite in the way that John expected.
- The tour guide who claims to have seen the hound is named Fletcher — presumably in reference to Bertram Fletcher Robinson, who originally gave Conan Doyle the idea for a ghostly hound.
- Holmes' reference to Watson as a "conductor of light" occurs in the original Hound of the Baskervilles. "Murder — refined, cold-blooded murder" is also lifted straight from the novel.
- The glowing bunnies are a nod to the original hound, which was painted with phosphorus to appear supernatural.
- The Grimpen Minefield is, of course, wordplay on the Grimpen Mire. The villains in both stories die trying to flee through it.
- Henry Knight's name is a play on the knight, Sir Henry Baskerville, from The Hound of the Baskervilles. Many of the other names are taken more or less straight from the original (the most obvious being Stapleton and Barrymore), including the surname of the original villain.
- Sherlock harpooning a pig carcass to solve a case comes straight from "Black Peter".
- When Sherlock is having his nicotine freak-out in the beginning, one of the places he looks for his hidden stash is in the toe of an old Persian slipper. This is where he keeps his pipe tobacco in the original stories (Watson mentions it in "The Musgrave Ritual").
- Sherlock's frustrated "I need something stronger than tea! Something 7% stronger..." is a reference to his famous cocaine habit in The Sign of Four, where he injected a 7% solution.
- Sherlock's remark about his mind being "like an engine racing out of control, a rocket tearing itself to pieces on the launch pad" when he doesn't have work echoes "The Adventure of Wisteria Lodge," where the original Holmes says "My mind is like a racing engine, tearing itself to pieces because it is not connected up with the work for which it was built."
- Sherlock spots the horse-racing section of a paper rolled up in the back pocket of a potential eyewitness. When the man is not forthcoming with his information, he pretends to have bet John that the man couldn't produce proof, and the man immediately gets very talkative. The original Holmes pulls the exact same stunt in "The Blue Carbuncle".
- "Once you've ruled out the impossible, whatever remains, however improbable, must be true," is a favourite Holmes Catchphrase employed in several of the original stories.
- Sherlock's remark that emotion is like "grit on the lens, a fly in the ointment", is a reference to the line "Grit in a sensitive instrument, or a crack in one of his own high-power lenses, would not be more disturbing than a strong emotion in a nature such as his" (From "A Scandal in Bohemia").
- Sherlock describes Lestrade as being "brown as a nut" (meaning his tan). This is a phrase used in A Study in Scarlet, although there it was Stamford describing Watson.
- The hallucinogenic fear gas is reminiscent of "The Devil's Foot", as is Sherlock's experiment with it, although in this case the results are merely emotionally traumatising rather than life-threatening.
- While suffering from the hallucinogen, Holmes sees Moriarty for a moment. Something similar happens in the Jeremy Brett adaptation of "The Devil's Foot".
- Sherlock's experiment on Watson also recalls a remark of Stamford's in A Study in Scarlet that he could imagine Holmes "giving a friend a little pinch of the latest vegetable alkaloid, not out of malevolence, you understand, but simply out of a spirit of inquiry...".
- Sherlock being asked to find a little girl's lost pet rabbit on the English moors is a reference to "Silver Blaze", where a client hired Holmes and Watson to find his lost racehorse on the English moors. Note that the pet rabbit's name is "Bluebell", which is a fairly common name for racehorses.
- The receipt John finds in the pub is from Undershaw Meat Supplies. Undershaw was the name of the home Sir Arthur Conan Doyle lived in when he wrote The Hound of the Baskervilles.
- When Sherlock says the "When you eliminate the impossible, whatever remains, however improbable, must be true" Watson calls him Spock. Spock quotes the same line in Star Trek VI: The Undiscovered Country, which was co-written by Nicholas Myer who also wrote The Seven Percent Solution — one of the most famous Holmes stories not written by Doyle.
- Never Found the Body: The body of the father, who was allegedly killed by the wolf, was never found. This fact doesn't become plot-relevant though.
- Nice Job Fixing It, Villain: Had Frankland not intervened and safely escorted Sherlock and Watson outside the Baskerville military base, neither of them would've been there to stop his plot of drugging Henry to the point of madness-induced suicide.
- Noodle Implements: The episode starts with Sherlock bursting into 221B Baker Street soaked in blood and wielding a harpoon:Sherlock: Well, that was tedious.
John: You went on the Tube like that?
Sherlock: None of the cabs would take me.
- For fans of the books, however, it's pretty clear that what he was doing was stabbing a pig carcass with the harpoon to work out how much effort is required to kill a person in a similar manner.
- Notable Non Sequitur: Sherlock specifically takes the case only because the witness uses the word 'hound' instead of 'dog'.
- Nothing Is Scarier:
- The sequence in which John is trapped in a lab with an apparently escaped hound.
- As well as the flood lights in front of Henry's house, and whatever the hell he's seeing in them.
- Not His Sled: The character with the original villain's name turns out to be a Red Herring who eventually helps Sherlock and John to solve the case, while the real villain has the name of an innocent bystander from the original novel.
- Not Quite Dead: The real hound at the end. Minutes after being shot it comes back and provides Dr Frankland with an opportunity to escape.
- Oh, Crap!:
Sherlock: [clutching a glass of whiskey and shaking badly] Look at me, John. I'm afraid.
- John has a pretty big one when he's trapped in the Baskerville lab in the dark and, as he tries and fails to get out, he hears the hound growling, evidently thinking the hound is trapped in there with him. When Sherlock finds him and gets him out, he's quite hysterical.
- At the end, Sherlock is trying hard to tell the hysterical and suicidal Henry Knight that the hound is actually a figment of their imagination brought on by hallucinogens, so none of it is real. Except a howl is suddenly heard again and a dark shape is moving along a ridge...
- Frankland has one when he realises he's stepped on a mine while trying to escape.
- Once More, with Clarity: Early on Henry's flashback to that night in the woods involves a fight between his father and a hound but at the end Sherlock makes him shed his Trauma-Induced Amnesia and this time the flashback shows us the father fighting with a man wearing a gas mask, who turns out to be Dr Frankland.
- Only Friend: Sherlock points this out to John, clarifying his assertion the night before that he doesn't have friends:Sherlock: Listen, what I said before, John, I meant it. I don't have friends. I've just got one.
- O.O.C. Is Serious Business:
Sherlock: [clutching a glass of whiskey and shaking badly] Look at me, John. I'm afraid.
- When Sherlock, in the midst of Going Cold Turkey, declares he will take on the case of Bluebell, a missing rabbit, John immediately gets up and gives him a packet of cigarettes.
- John is also weirded out when Sherlock makes coffee for him. He's right to be.
- It's a huge deal to see Sherlock and, to a slightly lesser extent, John, experiencing and expressing devastating levels of fear:
- Sherlock reacting with fear to the Hound, when he normally stays very distant from emotional responses. He notices himself that this is OOC behaviour, and deduces that he's been drugged.
- The Password Is Always "Swordfish": "Maggie". He could have at least added random numbers or something...
- Not only that but picking a line of sight password is one of the WORST things you could do.
- And the password isn't long enough to meet government security standards anyway.
- The choice of words, given Maggie's real-life support for people like Augusto Pinochet, could be a Take That! against governments all too willing to perform, accept or cover hideous acts.
- Real Life Writes the Plot: Sherlock knows that Lestrade just returned from holiday because of his tan. In real life, Rupert Graves was tan because he had just returned from Guadeloupe while filming Death in Paradise. His tan was written into the script.
- Red Herring:
- The Morse code John notices. It turns out to lead to a dogging site instead of anything relevant to the case, though it does at least provide Sherlock with a genuinely helpful "Eureka!" Moment.
- Dr Stapleton, especially for those familiar with the original novel. She's involved in genetic experimentation on animals of dubious legality, but is otherwise innocent — and her counterpart in the original turned out to be the killer.
- Repeat What You Just Said: The point when Sherlock gets interested in the case.Henry: Mr Holmes, they were the footprints of a gigantic hound!
Sherlock: Say that again!
Henry: I found footprints, they were...
Sherlock: No, no, no, your exact words. Repeat your exact words from a moment ago, exactly as you said them.
Henry: Mr Holmes, they were the footprints of a gigantic hound.
Sherlock: I'll take the case.
- The Reveal: The "monster dog" that killed Henry's father was really Dr. Frankland, seen through the eyes of a hallucinating Henry. Frankland and Henry's father previously developed a hallucinogenic chemical agent while working together on a CIA project called "H.O.U.N.D."; the chemical caused Henry to see Frankland as a monstrous dog because he was wearing a sweatshirt with "H.O.U.N.D." written on it.
- Room Full of Crazy: Moriarty's cell. Out of which Mycroft lets him.
- Scenery Porn: This episode sure makes (non-British) viewers want to visit Dartmoor.
- Separated by a Common Language: One character refers to his "cell" as opposed to a "mobile". This is an important plot point.
- Holmes' idea that H.O.U.N.D. is in the sugar comes straight from the Second Doctor episode "The Moonbase" in which the Cybermen's virus was in the crew's sugar.
- The screaming monkeys in the lab coupled with the insane aggression of those exposed to H.O.U.N.D for too long are possibly a reference to 28 Days Later.
- The Shrink: Dr Louise Mortimer. While she genuinely cares about Henry Knight, she doesn't realize that the delusions she believes he's suffering from are caused by witnessing the brutal murder of his father and then being regularly dosed with an experimental psychotropic drug. In her defence, nobody would have reason to suspect that given it was all classified and Sherlock himself wasn't thinking of it until he experienced the Hound as well.
- Stuff Blowing Up: Grimpen Minefield and Dr Frankland's fate.
- Stupid Sexy Flanders: John commenting on Sherlock's cheekbones. Sherlock has the decency to just look confused.John: You being all mysterious with your — cheekbones. And turning your coat collar up so you look cool.
- Suicide, Not Murder: Sherlock apparently drew this conclusion when he and Watson played the board game Cluedo, thinking it's the "only possible solution".John: It's not actually possible for the victim to have done it, Sherlock!
Sherlock It was the only possible solution!
John: It's not in the rules!
Sherlock: "Then the rules are wrong!"
- Surprise Inspection Ruse: Sherlock enters the Baskerville facility by pretending to be an inspection from Home Office. He even uses his brother's entry card to prove his claims. While Mycroft learns about the incident and proceeds to warn Baskerville's commander, Sherlock still has enough time to see what he wanted.
- There Are No Coincidences: Inverted when a joke about a little girl's escaped rabbit turns out to be part of the A-plot. "People say there's no such thing as coincidence. What dull lives they must lead."
- Trauma-Induced Amnesia: While under the effects of a hallucinogenic chemical Henry watched his father being murdered by a scientist; the 'hound' was something his mind invented from surrounding clues to cope with the trauma.
- Vader Breath: The true killer is doing this through his red-eyed gas mask.
- Villain: Exit, Stage Left: Subverted. Once Frankland is caught, he attempts to escape through the Grimpen Minefield, only to end up stepping on a mine and getting blown up.
- What the Hell, Hero?: In this episode, Sherlock has gone from violently defending Mrs Hudson and showing a lot of affection for her to cruelly telling her a man she's involved with is a bigamist and threatening her with a harpoon- all because John won't tell him where his emergency cigarette stash is. John is so horrified by his behaviour that he shouts at him and then, when she has tearfully retreated, orders him to go downstairs and apologise to Mrs Hudson.
- White Bunny: Justified: The rabbits Dr Stapleton is working on are pure white: genetically engineered lab animals are usually white because it's easier to see bioluminescence in a light-coloured specimen than in a darker one.
- Your Mind Makes It Real: The experimental drug acted as a fear stimulus that ended overwhelming and killing the test subjects.
- Your Television Hates You: Henry, whose father was apparently killed by a wolf, keeps getting wolf-related channels. Justified, as he's under the influence of a fear-inducing drug.