'Sherlock' season 4 spoilers news: What we know so far about 4th installment

With about half a year to go before "Sherlock" season 4 hits TV screens, fans of the series are trying to figure out what it has in store for them. Here's what is known about the show so far, thanks to the synopsis that BBC recently released.

"Season 4 begins with the mercurial Sherlock Holmes (Benedict Cumberbatch), back once more on British soil as Doctor Watson (Martin Freeman) and his wife Mary (Amanda Abbington) prepare for their biggest challenge yet: becoming parents."

In the upcoming installment, it looks like everybody's favorite detective and his sidekick would be facing their old foe, Jim Moriarty (Andrew Scott), once again. However, they would also be facing one of their toughest, creepiest enemies to date (to be played by Toby Jones), one that co-creator Steven Moffat described as "the darkest villain" the series has ever had, stating the "guy is the purest evil."

Apparently, Sherlock would come home to London prematurely from a forced exile. He would reunite with Doctor Watson and the latter's wife, Mary, in the process. They would try to stop Moriarty together, according to the report by the International Business Times.

What's worth noting about the upcoming season is the premise of the story, which Cumberbatch described would be "myopically dark."

"You're talking about the end of the universe darkness. You can't see in front of you and would walk into everything dark," the actor told Collider during the San Diego Comic-Con.

"It's the same show. Hopefully, there are lots of laughs and lots of great personal stuff, but it is explicitly a darker season. You'll have to wait and see," added co-creator Steven Moffat.

Cumberbatch and Watson would still provide the necessary comic relief, but Amanda Abbington, who plays Mary Watson on the series, said her role would be "juxtaposed with humor."

"Sherlock" season 4's stories would all be based on original books by Arthur Conan Doyle "to a greater or lesser extent," according to Moffat. The series would return in early 2017.