There’s plenty of hidden clues, meta references and nods to Arthur Conan Doyle’s original detective stories in BBC’s Sherlock. But now one eagle-eyed fan has spotted a very bizarre Easter egg in 221B Baker Street: a letter from Torchwood. 

Remember the bit in the last episode, The Lying Detective, when Watson discovers the package containing the DVD Mary Watson sent to Sherlock? Well, on the mantelpiece – the same one where Mrs Hudson says the sleuth keeps “things he can’t figure out” – is a postcard brandishing the Torchwood ‘T’ logo.

See it?

Can’t think of why the Cardiff alien-busting Torchwood would feature in Sherlock (apart from Jack Harkness warning Holmes that Watson’s baby is actually an extraterrestrial)? Well, there have been some fun Doctor Who references plugged into the show before: turn your microscopes on the promo image for series four and you can see a book written by Lavinia Smith i.e. the aunt of Who companion Sarah Jane Smith.

And here’s a bonus egg for your basket: there’s also a letter addressed to “S Holmes at 156 Montague Street” on the mantelpiece. In the original Sherlock Holmes story The Gloria Scott, it’s revealed that Holmes first lived at Montague Street before moving to Baker Street. In other words, whatever is in that envelope has been puzzling Sherlock for years.

We can only hope everything on that mantelpiece, including a way to contact the immortal Captain Jack Harkness, might be able to help Sherlock take on the elusive Euros. Well, presuming Baker Street doesn't blow up first, that is.

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