You and John Watson were old flames back in your high school year. Thankfully, when you broke up, you still remained friends. That was, until the year of the war came around. While John went to war, you began to tend to your dying sister, who you knew only had a few more years. John and you kept in touch, but the letters started to get more and more infrequent as the war began to get more and more brutal.
After your sister died, you moved to London, hoping for a fresh start and to eliminate any memories of your her. The next thing you know, three people get murdered right before your eyes, and guess who shows up to inspect? John Watson. And his friend, Sherlock Holmes.
You took a liking to Sherlock, despite his arrogance and sociopathic tendencies, and you slowly begin to see his feelings that he hides underneath his shell.
When he sees how clever you are, Sherlock also takes a liking to you, but tries his hardest to hide it. He knows that sentiment is a chemical defect found on the losing side.
Now you, Sherlock and John Watson are solving cases together, but what happens when the person you fear most shows up and starts to torment John and Sherlock.