'Sherlock' season 4 air date, plot spoilers: Producers hint upcoming season based on Doyle's 'The Speckled Band'?

Until now, very little is known about the plot of the upcoming BBC series "Sherlock" season 4. Fans have been theorizing, but producer and writer Mark Gatiss, who stars on the series as Sherlock's brother Mycroft Holmes, said none of fans' theories are hitting the target.

Now, there are rumors that hidden clues may be found in one of Sir Arthur Conan Doyle's novels, "The Speckled Band." Both Gatiss and co-producer Steven Moffat implied in a recent interview that much of Doyle's "The Speckled Band" was woven into "Sherlock" season 4's storyline.

According to The Huffington Post, Gatiss promised that new clues about the Benedict Cumberbatch starrer will be revealed leading to the fourth season's premiere in January. The outlet likewise recalls what Moffat earlier stated, that those who want to understand "Sherlock" season 4's arc should read the above-mentioned canon.

Still, the report should be taken with a grain of salt, because for all the fans know, it could be something meant to derail their theories about the upcoming season. Both the producers and star of the show have hinted that season 4 will be twisted, what with Sherlock's toughest nemesis thus far, Culverton Smith (Toby Jones), making things miserable for the beloved detective.

In an interview with Collider a couple of months back, Cumberbatch himself said that "Sherlock" season 4 will be very dark. Apparently, aside from Smith, Sherlock's age-old rival James Moriarty (Andrew Scott) will be back, too. Moreover, there are speculations that Mary Watson (Amanda Abbington), John Watson's (Martin Freeman) wife, is actually a secret ally of Moriarty.

Meanwhile, Moffat revealed that "Sherlock" has received countless offers from other networks that want to capitalize on the success of the series. Nevertheless, he and his co-producers chose to stay with BBC.

"We have had offers. That's not what it's about," he told Press Association via Digital Spy. "It should never be about that."

He likewise acknowledged BBC's stand not to give in to massive (read: expensive) deals presented to them, saying, "I think the BBC was quite right not to reward greed. It's wrong."

"Sherlock" season 4 is expected to drop in on BBC in January 2017.