Watch the Sherlock Season 4 Teaser

Check out the dark first trailer for the upcoming season of BBC’s Sherlock, which was released at this year’s San Diego Comic Con.

According to a report by IGN, the Sherlock SDCC panel featured star Benedict Cumberbatch, Amanda Abbington (Mary Watson), and executive producers Mark Gatiss, Sue Vertue, and Steven Moffat. During this panel, they released the first official trailer for the new season of the detective drama.

“The roads we walk have demons beneath,” warns Mycroft (played by Mark Gatiss) ominously, “and yours have been waiting for a very long time.”

A scruffy looking Sherlock spends most of the clip brooding over the return of an old enemy and a new, mysterious threat. The trailer features appearances from many of the Sherlock main cast including John Watson, Molly Hooper, Mycroft Holmes, Mrs. Hudson, and Inspector Lestrade.

There is also a first glimpse at Toby Jones, who was cast as the season’s antagonist.

“We’re going to have endless fun, Mr. Holmes, are we?” Jones’s character says menacingly.

“Oh, no,” Sherlock replies coolly, “no, not endless.”

The rest of clip has scenes of helicopters, prison cells, assassins, explosions, and hospitals, proving that the next three episodes of the show will be even bigger than ever.

“Everything they know will be tested,” the trailer warns gravely, “Everyone they know is under threat.”

Abbington discussed season 4 during the panel, saying:

“It’s really dark…It’s the darkest that Steven [Moffat] and Mark [Gatiss] have written. When we read them, all of us, when we read them we were kind of overwhelmed, I think.”

Cumberbatch also added:

“It’s a genuine emotional rollercoaster… And the learning curves are massive.”

Moffat previously hinted that this new season may possibly be the last for the show.

Sherlock season 4 will be out in 2017 on BBC One.

Check out the trailer below: