Who is Mary? In season 3 and 4 much has been revealed.   Her real name is not Mary Morstan, her accent is currently English, but Sherlock suspects she is not. She worked for an intelligence agency and she was a member of AGRA.

What other secrets of her past are there?   Magnussen had information on her and there was also a flash drive. Both are lost, but will there be another way to find out? Are there any more copies of the flash drive?

On a side note: It is not the first time a female character has a secret past. What is remarkable is that so often the secret is   that they work for an intelligence agency: Laura Bristow (Alias), Doris McGarrett (Hawaii Five-O), Rita (Castle), Katarina Rostova (The Blacklist).

Coincidence?

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