Sherlock AU Part 3: The problems of your future are my privilege.
Mary and Sherlock narrowly escape the trouble they caused while dealing with the corrupt businessman from Mary’s former life, with the help of Mycroft Holmes, Sherlock’s big brother, who occupies a minor position in the British government. Mary is able to ride out the rest of her pregnancy with no issues and gives birth to a beautiful baby girl they name Rosamund. While Mary and John get used to domestic family bliss, Sherlock occupies himself with a case from Mycroft that leads to yet another face from Mary’s past, only this time this face is bent on revenge for what he thinks is a betrayal from Mary during a failed mission. More secrets are revealed about Mary’s former life as a super agent. Mary tells Sherlock about the failed mission and thinks she can reason with her former associate. Sherlock vows to keep Mary safe but this is one mission she must do alone.
Sherlock and John intercept the lone wolf at a location and they talk her into going home with them so they can keep her and Rosamund safe. Just as Mary agrees, all three of them are confronted by the former agent who has tracked Mary every step of the way, so he can take his revenge. A gun battle ensues and the disgruntled agent is killed before Mary could explain what happened that fatal night at the embassy. With the former agent dead, there are still questions as to why the embassy mission failed. Something doesn’t seem quite right and Sherlock asks Mycroft to do some digging and it leads them to the real person who betrayed Mary’s team. When Sherlock and Mary confront the person responsible for the failed mission, (a secretary on Mycroft’s staff) and she decides to Shoot her way out of the confrontation. Sherlock is in the line of fire and Mary, with her agent readiness never ever being gone, does the one thing she’s always been prepared to do. In doing so, she is killed while saving Sherlock’s life.
Mary leaves behind one last message for Sherlock and reminds him that the danger is the fun part but he can’t outrun that forever. She asks him to take care of John and Rosamund and reminds him that 221b is the last refuge for the desperate, the unloved and the persecuted.