As we’ve previously reported, Benedict Cumberbatch, Martin Freeman, and their hit BBC show Sherlock are heading back in time for this year’s Christmas Special. The one-off 90-minute episode will transport Cumberbatch’s brilliant-yet-sociopathic Sherlock Holmes and Freeman’s average-yet-likable John Watson to Victorian London, which is the sort of clever twist that could only be conjured up by modern television writers. Most of the details about the special—like whether or not there’ll be any explanation for why the show suddenly takes place in a different era—haven’t been announced yet, but the BBC has released a promo image of Holmes and Watson in some retro outfits that should act as a suitable tease for Sherlock fans.

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Let’s all put on our deerstalker hats and try to deduce some clues about the special from this image. Why does Watson have a mustache? Is Holmes cranky about something? Watson’s pose looks a little awkward, is he uncomfortable? Obviously, the solution to all of these questions is right in front of our eyes: Watson has his leg up and his hand on his hip to subtly reference the month of December, and there’s an ink smudge on the back of Holmes’ left hand that clearly depicts the number 25. Therefore, this Sherlock special will air on December 25 in the U.K. There are no clues about when it will air in America, though, because we don’t know that yet.