Lock and Key (BBC Sherlock fan fiction)

When her mother dies in a car accident in America, Sadie Watson must travel to London to live with her Uncle Watson. In an instant she is thrown into the world of Sherlock Holmes and John Watson.

Yet everything isn't just murder and finding Sadie an appropriate place to sleep. SHIELD is starting to inquire to 221B Baker Street, and Sadie Watson must come to terms with a hidden past.