Of course, every episode of Sherlock contains references to the original Sir Arthur Conan Doyle stories, from titles and plot devices to villains and their schemes. But some are less obvious than others. There are those obscure lines of dialogue, the red herrings that may initially send fans in the wrong direction and the neat little nods that will delight them.


Series four opener The Six Thatchers has all of the above. How many did you spot?

“You see but you do not observe”

Holmes’s words to Watson in the first of Sir Arthur Conan Doyle’s Sherlock Holmes short stories make a serious point about how the detective has trained himself to view the world.

"You see, but you do not observe. The distinction is clear. For example, you have frequently seen the steps which lead up from the hall to this room... how many are there?"

"How many? I don't know."

"Quite so! You have not observed. And yet you have seen. That is just my point. Now, I know that there are seventeen steps, because I have both seen and observed.”

In The Six Thatchers the same phrase is used beautifully to prick Sherlock’s pomposity – or perhaps to demonstrate that he is capable of making fun of himself after all – and creates one of the funniest moments of the show so far.

As Sherlock unfurls his criticism of “Watson” it’s not until the camera reveals baby Rosamund in John’s armchair that we realise it is Watson junior, not senior, Sherlock is berating.

“As ever Watson, you see but do not observe. To you the world remains an impenetrable mystery whereas to me it is an open book. Hard logic versus romantic whimsy, that is your choice. You fail to connect actions to their consequences. Now, for the last time, if you want to keep the rattle, you do not throw the rattle.”

Appointment in Sumatra

Woven throughout the episode is the fatalistic fable Appointment at Samarra, about an unavoidable meeting with the Grim Reaper. When it's first mentioned, Mycroft reveals that as a boy Sherlock wrote his own version, called Appointment at Sumatra. In the original stories, Holmes mentions in passing a case that "the world is not yet ready for", that of the Giant Rat of Sumatra. It's a story Doyle never wrote and that we know nothing else about but it's a favourite of Sherlock Holmes fans nonetheless, and that includes Sherlock writer Mark Gatiss, hence the reference. In fact, there was also a nod to it in series three. One of Gatiss and co-creator Steven Moffat's key word clues to the episodes was 'rat' and turned out to relate to a street name, Sumatra Road.

“I thought you’d done something clever”

Just like a magician revealing the secrets of an astounding trick, when Sherlock explains his deductions certain people decide there's actually nothing impressive about them after all.

In the Adventure of the Red Headed League, one of Holmes’s clients, a Mr Jabez Wilson, is flabbergasted when the detective deduces from a quick glance “that he has at some time done manual labour, that he takes snuff, that he is a Freemason, that he has been in China, and that he has done a considerable amount of writing lately”.

But when Holmes explains the lightning quick chain of observations and deductions that have led him to his conclusions, "Well, I never!" says Wilson. "I thought at first that you had done something clever, but I see that there was nothing in it, after all."

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The same thing happens in The Six Thatchers when Sherlock explains to a client how he knows so much about him. “I thought you’d done something clever but it’s simple innit?”

No, it’s not simple. You’re simple.

The Black Pearl of the Borgias

This lovely little red herring pops up throughout The Six Thatchers, with various characters assuming that Sherlock is trying to solve the case of the infamous stolen jewel, although he actually has no interest in it whatsoever.

One of the key elements of The Six Thatchers is based directly on the Sherlock Holes short story The Adventure of The Six Napoleons. In Thatchers, an all-important memory stick has been desperately hidden in one of half a dozen busts of the late prime minister. In Napoleons, it really is the valuable Black Pearl that the thief is looking for, as he rampages around town smashing up the statues in his attempts to find it.


We first saw the acronym A.G.R.A. in series three finale His Last Vow on the aforementioned memory stick containing the truth about Mary’s former life. In The Six Thatchers we learn its full significance, and what A.G.R.A. stands for. Each letter is the first initial of the four people in Mary’s group of black ops mercenaries: Alex, Gabriel, Rosamund (Mary’s real first name, which she has now passed on to her daughter) and Ajay. They each have a stick containing proof of everything they’ve done together, meaning none of them will ever betray the other for fear of the damning information being leaked.

In original Sherlock Holmes story The Sign of Four, the Agra treasure is a great hoard of pearls and jewels stolen from the Indian city of the same name, but there’s a similar principle in play since the treasure was to be equally divided between four men who each made a pact not to betray the others. In many ways, the Six Thatchers is as much based on The Sign of Four as it is The Six Napoleans. Speaking of which…

Toby the dog

Stubborn bloodhound Toby spends most of his time in The Six Thatchers sitting on a pavement refusing to move. That wasn’t the intention, as Mark Gatiss and Steven Moffat revealed during the Q & A following a screening of the episode – in fact they were forced to quickly write the pavement scene in during filming in order to account for the fact that the dog wouldn’t follow the script.

In the original stories, Toby appears in The Sign of Four but rather than a bloodhound is described by Watson as an "ugly long haired, lop-eared creature, half spaniel and half lurcher, brown and white in colour, with a very clumsy waddling gait" but by Holmes as more helpful than "the whole detective force in London". Unlike Toby the bloodhound.

Reigate Square

Blink and you’ll miss it but this is the name of a Chinese restaurant seen on a take-away menu pinned to Mycroft’s fridge just before he makes the call to the mysterious Sherrinford.

What does it have to do with the original Sherlock Holmes canon? Well Reigate Square sounds a lot like The Reigate Squire, the name of a short story that appears in The Memoirs of Sherlock Holmes.

Just say ‘Norbury’

In Conan Doyle story The Adventure of the Yellow Face, Holmes rushes too quickly to a conclusion and misses the exact solution to the case, which lies in a cottage in the town of Norbury, south-west London. Afterwards, he tells Dr Watson, "if it should ever strike you that I am getting a little overconfident in my powers, or giving less pains to a case than it deserves, kindly whisper 'Norbury' in my ear, and I shall be infinitely obliged to you."

In The Six Thatchers, the cost of Sherlock’s failure is much higher. Mary is killed saving Sherlock when she jumps in front of a bullet from the gun of disgruntled secret service desk jockey Vivian Norbury. Afterwards, he asks Mrs Hudson “if you ever think I’m becoming a bit full of myself, cocky or overconfident, just say the word ‘Norbury’ to me would you. Just that. I’d be very grateful.”


This article was originally published in January 2017