The fourth series of the BBC's hit Sherlock won't air until 2017, but attendees at the show's San Diego Comic-Con panel got a nice surprise when the assembled cast and crew revealed the first trailer for the mysterious new episodes.

Get it? Mysterious? Because they're mysteries?

Anyway... Even if you're not up to speed on the show, you're probably familiar with master detective Sherlock Holmes (Benedict Cumberbatch) and his trusty best friend Dr. John Watson (Martin Freeman). The modern reinvention last left off with their arch-enemy Moriarty (Andrew Scott) seemingly returning to life after shooting himself in the face; and threatening all of England with his resurrection.

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In the 2016 Christmas Special "The Abominable Bride," though, Sherlock concluded that Moriarty was not alive — but that he also knew exactly what the master criminal had planned next.

The baffling cliffhanger will be complicated in series four by the addition of another villain from Arthur Conan Doyle's stories, played by Toby Jones. Will Holmes and Watson be able to stop both criminals at the same time? Probably, but we'll just have to stay tuned to find out.

In addition to the new trailer, the panel also showed off a fun video explaining how they chose who got to go to Comic-Con:

Sherlock returns to the BBC in 2017, and will most likely debut on PBS soon after that.