One of the great twists of Series Three was the true identity of Mrs Mary Watson. Discovered by Sherlock in Magnussen's office, it turns out that she's an assassin! Perhaps the most worrisome aspect of this series was the inclusion of Mary Morstan as Watson's wife - surely she would ruin all the fun of Sherlock and John's dynamic duo? Thankfully, this was not the case as Mary proved a fantastic character. Ably played by Martin Freeman's real-life partner Amanda Abbington, Mary was a level-headed woman who encouraged her husband's involvement with Sherlock without butting in. It was of course a massive surprise, then, when we found out that John had fallen in love with a psychopath - again. With all the clues hidden in plain sight despite no one guessing it, this scene is a real coffee-spluttering moment and also a great example of the level of intelligent and exciting storytelling that Sherlock delivers. But there was a bigger twist coming...
