***As always, SPOILER ALERT***
Mary Watson dies. That is what happened in the original work by Sir Arthur Conan Doyle. Dr. John Watson’s wife dies.
In The Memoirs of Sherlock Holmes, Sherlock “dies.” When he returns in The Return of Sherlock Holmes, Mary Watson is dead.
Am I saying that will happen in the BBC show? No, I am not saying I am 100% certain it will happen, but if I were to bet on it, I would bet that she would.
There is no mention of how she died in the books, and if there is one thing Gatiss and Moffat like it is ambiguity. Imagine what they could do with the death of Mary. I think they would pattern it after “The Adventure of the Dancing Men.”
I recently read that short story and I could not help but notice some similarities. Sherlock’s client in this story explains that his wife when she married him said that she had a shadowy past, but that the future was bright, and she would always be honest with him as long as he never asked about her past. Sound familiar? It should.
"The problems of your past are your business. The problems of your future are my privilege." - Dr. John Watson, Sherlock, “His Last Vow”
I suspect that Gatiss and Moffat have had this in the works. They set up that whole “Let’s just pretend your past never happened” thing in S3E3, and I suspect they will follow through with a death similar to that story in the next season.
In the original story, the wife becomes afraid when contacted by someone form her past. The husband does not want to betray her trust in order to obtain details, and he quietly contacts Sherlock Holmes for answers. After decipher codes left for the wife, Sherlock rushes to their houses, but before he can get to them with his warning of danger, tragedy occurs. The man from the wife’s previous life enters their house one night and is shot at by the husband. He misses and is killed by the man, who then escapes out of the house. The wife, out of grief, shoots herself, but does not die.
Here is how I see that playing out on the BBC:
Someone form Mary’s past resurfaces.Perhaps, it is an associate or employee of CAM, or perhaps, Moriarty has reasons to go after her. John gets worried, and Mary reminds him of his promise. John (unlike the husband in the story) presses the matter, and they fight. The stranger confronts Mary, and she gets killed, as does their baby. John becomes racked with guilt over arguing with her before her death and not being there to protect her and the baby. I do not think they will want to air a suicide attempt by Watson, so he will either become so depressed he cannot function or he goes mad with rage and seeks a bloody revenge.
One thing working for me in this theory is the whole baby thing. I do not see “Mr. and Mrs. Psychopath” (as CAM called them) settling down and being parents, especially not Mary. I think the writers will kill off both Mary and the baby, and I believe they will use the basic idea I have set forth and make much more epic than I made it seem.