Is Sherlock over or will there be a fifth season?

Sherlock series four: Five questions after last night's episode

9 January

Warning: spoilers for series four ahead.

BBC1's Sherlock has delighted and confused viewers in equal measure with its latest episode, which featured a seemingly unhinged Sherlock, a drug-fuelled plot and a disturbing new villain - or two.

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The Lying Detective touched on some familiar themes, with Benedict Cumberbatch's hero playing out a risky strategy to catch the evil Culverton Smith (Toby Jones), Dr John Watson (Martin Freeman) struggling in vain against Sherlock's magnetic pull and Sherlock flirting with a deadly drug addiction, only to triumph in the end thanks to his superior intellectual powers.

Despite covering some well-trodden ground, the rapid-fire episode, filled with in-jokes and mental backflips, sent viewers into a frenzy of frustration as they tried to figure out what was going on.

Others , however, were dazzled by what they saw as a return to form for the series following the season opener, which saw the dramatic death of Watson's wife Mary (Amanda Abbington) but seemed to treat its detective plot as an afterthought.

The Lying Detective put Sherlock's detection skills to the test, but also left fans with a series of puzzles to solve. Here are five key questions raised.

Is Euros really Sherrinford?

The big revelation came when Watson's therapist (Sian Brooke) exposed her true identity. After masquerading as his counsellor, the mysterious "E" on the bus and Culverton Smith's daughter Faith, the woman revealed she was actually Sherlock's sister, Euros.

So far, viewers had been led to believe there is a missing Holmes brother called Sherrinford - so are Euros and Sherrinford the same person? Or are there a long-lost brother and a sister? It's worth noting, as Sherlock points out earlier in the episode, that people always stop counting at three.

Did Euros shoot Watson?

The final moments of the episode seem to show Euros shooting Watson, but is this just another trick? Surely she would have killed him, after firing from such a short range? But a quick peek at the trailer for next week's episode seems to show Watson alive and well and telling Holmes to "keep it together".

Then again, we've just sat through an entire episode in which dead Mary appeared and advised Watson on how to deal with Sherlock, so anything's possible.

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What's the relationship between Euros and Moriarty?

For some time now, "Miss Me?" has been a catchphrase associated with the threatened return of Moriarty. But this episode left us wondering if it was really a trick orchestrated by Euros.

Sherlock warned of an "east wind coming" a few moments before the "Miss Me?" reveal in the series three final, His Last Vow. In The Lying Detective, we discover not only that the name of Sherlock's sister Euros means the east wind, but that Euros wrote "Miss Me" in invisible ink on the piece of paper she gave Sherlock as a clue to the Culverton Smith case.

So is Euros linked to Moriarty, or does she have a sinister plot of her own?

Why didn't Sherlock recognise Euros?

It seems quite a big plot hole that Sherlock didn't recognise his own sister. We can perhaps explain John failing to notice that the woman on the bus was also his therapist because of his distressed state, but Sherlock usually has an eye for detail that others miss. However, perhaps he doesn't know her very well - did they lose contact as children? Euros doesn't seem to know Sherlock very well neither. When she met him in the guise of Faith, she said he was nicer than she thought he would be.

What does Redbeard have to do with it all?

Sherlock, in a drug haze, had yet another vision/dream about the dog Redbeard, the flashback showing a child in wellington boots running with a red setter dog, seeming to cause the detective some distress. So is there a link between the dog and Sherlock's long lost sibling - or siblings?

Episode three of Sherlock airs on BBC1 at 9pm.

Sherlock season 4: Does Moriarty have accomplices? Five intriguing fan theories

5 January

Spoiler warning: this article contains details about the first episode of season four of Sherlock Sherlock's much anticipated fourth season premiered on New Year's Day with a twisty, mind-bending episode that sent fans into a frenzy of speculation over where the new season is headed.

The Six Thatchers was a classic piece of fan service, crammed with in-jokes, literary references, confusing retroactive plot and a killer twist that saw Amanda Abbington's Mary make a dramatic exit.

Viewers have since flooded social media boards with what might happen next. Here are five of the most intriguing theories.

The "other woman" is not what she seems

Fans were more than a little shocked and disappointed to see new father John Watson flirting with a mysterious woman on the bus. She gave him her number, signed with the initial E, and the two began texting each other.

But did they? Several fans argue this is what we're meant to think and not what actually happened.

Others say "E" was wearing a rather unconvincing red wig and may in fact be in disguise.

There is also a school of thought that she is linked to Sherlock's nemesis Moriarty and was using the text exchanges to make Watson vulnerable.

There is also speculation that it was a little too convenient for Watson to start flirting with a new woman just before losing Mary - and why didn't Sherlock, so good at spotting marital infidelities, pick up on the flirtation?

What does it all mean? No one is sure about much at this stage, other than we're bound to see more of "E" - and you probably shouldn't trust women who give you their phone numbers on public transport.

There’s another Holmes brother

Ever since Mycroft dropped a hint about a possible sibling at the end of series three ("I'm not given to outbursts of brotherly compassion. You know what happened to the other one"), fans have been holding out to see if another Holmes child appears.

At the end of The Six Thatchers, Mycroft telephone someone called Sherrinford - a name Sherlock Holmes author Sir Arthur Conan Doyle was originally planning to use for his detective.

While the name never crops up in the original stories, it has been linked to a third brother by writer and Holmes scholar William S Baring-Gould.

Will Sherrinford turn up later in the series? And why haven't we heard from him so far? Could he be the Holmes brother who went rogue?

Mary's last words are a clue

If you hung around for the end credits, you would have seen another snippet from Mary's beyond-the-grave message telling Sherlock to "go to hell". Is there more of the video that we haven't seen? And does she really mean the devil's home or is it a clue for the detective?

According to the fan theories, as Mary doesn't sound angry in the message, it's either the name of a place or a piece of coded information about Moriarty.

Moriarty has accomplices

Some have pointed out that Norbury, the jealous secretary turned traitor, actually repeats a line used by Moriarty in a previous season: "Why does anyone do anything?" Could it be possible that she was an accomplice of the master criminal, or someone he set in motion long before his apparent death?

And what about the mysterious DI Hopkins, who suddenly showed up and started flirting with Lestrade. Sherlock warned the police officer she wasn't the woman for him - but could she be one of the show's next baddies? Maybe she's working for Moriarty, or an unwitting stooge for one of his sinister plans?

The dog is a clue to Holmes's past

After being drugged by Mary, Sherlock was seen dreaming about his childhood pet, a red setter called Redbeard, a pair or red boots and two boys in the countryside – were they Sherlock and Mycroft?.

Then, at the end of the episode, he told a psychiatrist that he has a recurring dream. Is it about Redbeard?

Sherlock's old pet was first mentioned in series three and the detective also muttered the name at seeing a dog in The Abominable Bride. Redbeard is also written several times in Mycroft's notebook.

This type of repeated clue always has a meaning, so will it reveal something about Sherlock's past? Did something bad happen to the dog? Is it a clue about the third Holmes brother?

The next episode of Sherlock, The Lying Detective, airs on BBC1 on 8 January at 9pm, with The Final Problem following a week later.

Sherlock series four: New BBC trailer has fans 'buzzing'

27 October

A new trailer for Sherlock series four has sent fans into a frenzy - but will this be the last they see of the BBC's detective for a while?

Viewers savouring the last crumbs of the Great British Bake Off final were the first to see the television teaser, which was aired immediately after the cooking contest finished.

The 90-second film is similar to the one that appeared online after Comic Con in July, but includes a black screen and the numbers 01.01.17, confirming the premiere date of 1 January 2017.

It also appeared on the official Twitter account for the series.

Fans were given a glimpse of upcoming scenes, along with the mysterious lines: "Everything they know will be tested... Everyone they know is under threat."

The trailer offers a sneak peak of The Six Thatchers, an update of the Arthur Conan Doyle story The Six Napoleons. It is the first of three episodes, including The Dying Detective and an as-yet-unnamed episode.

However, Sherlock actor Benedict Cumberbatch, who is currently attending premieres for his new Marvel film Dr Strange, hinted it might be a while before viewers get to see the detective in a fifth series.

The actor revealed this week that the upcoming episodes will be so dramatic fans might require a break afterwards.

"I think there will be a lull. I don't think it will be in a year and a half necessarily, but we will wait and see and maybe it will be," Cumberbatch said.

"First and foremost we have got a fourth series for people to watch and understand and when they watch it they might go, 'Oh yeah, maybe there does need to be a break now' because of what happens in it," he added. "No spoilers."

Sherlock series 4: New episode titles spark fan theories

27 September

Episode titles for the fourth season of Sherlock have been revealed, sparking fan theories about what's in store for viewers.

But has one of the cases already been solved?

BBC1 tweeted the titles of the first two episodes of the three-part series - The Six Thatchers and The Lying Detective – at the weekend.

As with previous seasons, the titles reference Arthur Conan Doyle's original 56 Sherlock Holmes short stories.

Tolly Wright at Vulture suggests The Lying Detective could refer to The Dying Detective, a story in which Sherlock – played in the series by Benedict Cumberbatch - pretends he is about to die. It includes the character Culverton Smith, who will be played by Toby Jones.

Meanwhile, The Six Thatchers could refer to The Adventure of the Six Napoleons, a story about a criminal who destroys busts of Napoleon.

The title ties up with the "Thatcher" tease announced at this year's San Diego Comic-Con, "which had fans theorising about former UK prime ministers, rural roofers and brands of bottled cider", says Louisa Mellor at Den of Geek.

She agrees there must be a link to The Six Napoleons, "a Lestrade-heavy case" involving the search for a hidden pearl.

But has the plot for the "Six Thatchers" episode already been revealed online? asks Paul Jones in Radio Times.

The title refers to a case Sherlock has already solved, says Jones, pointing to Dr Watson's official BBC blog, in which he discusses cases we've seen on screen, as well as others mentioned in passing.

In the blog, Watson (Martin Freeman) describes a case similar to the Conan Doyle story of the six Napoleon busts, but where the Napoleons have become busts of Margaret Thatcher and the item hidden is a penknife used in a murder. The basic premise is the same and the culprit in both is an Italian named Beppo.

Could this be the plot of The Six Thatchers we're about to see? Jones thinks this is unlikely, given how rigorous Sherlock creators Mark Gatiss and Steven Moffat are about secrecy. It's more probable, he says, that the mischievous pair have a different plot and have chosen the title to see if anyone picks up on it. Still, he adds, it's odd they would have two cases out there with the same name.

The further you dig, says Jones, "the harder it is to fathom exactly what's going on here".

We shall have to wait until January 2017, when Sherlock is aired in the UK, to find out the truth.