Sherlock has been testing the patience of its fans over the past two years and counting, but season 4 seems like it will be well worth the wait.

The first teaser shows signs of a dark and dangerous mystery — one that possibly involves a villain thought to be dead.

The trailer features Sherlock mulling over the return of a familiar foe, plus glimpses of Watson, Molly, Mycroft, Mrs. Hudson, and more, and warns that “everything they know will be tested. Everyone they know is under threat.”

The panel featured star Benedict Cumberbatch (Sherlock), as well as Amanda Abbington who plays Mary, and executive producers Mark Gatiss, Sue Vertue, and Steven Moffat.

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