Sherlock Series 4: 8 Huge Predictions (And Why They Need To Happen)
2. There's A Big Mary Watson Twist Coming
As mentioned, there's a bunch we don't know about the character of Mary Watson, but what we do know is that she's something of an enigma, even to Sherlock. Her CIA past means her connections and loyalties are constantly up for question, and though it seems like she genuinely loves John, that's not to say her affection isn't a fortuitous side effect.
In fact, it's quite possible that Mary will be revealed to be working for Moriarty. There a bunch of reasons why this might be the case, one of which lies in her name. Moran is a character written by Arthur Conan Doyle, an enemy of Sherlock's whose threat is second only to Moriarty. Mary's second name is “Mor(st)an”, which couldn’t potentially be a corruption of Moran in order to fool fans.
Series Three also contains an interesting visual clue: Mary is seen giving the thumbs up while a pair of thorns sprout from the top of her head. Mary very well may factor into Moriarty's posthumous plan, assigned to infiltrate Sherlock and Watson and ending up genuinely falling for John. Oh, and what does Moriarty “say” when he returns? "Miss Me": Miss M(ary) E(lizabeth).