I know I rec'ed this last year, but it's now a completed fic, and it's amazing! Truly one of my favorite fics ever.
How the mouth changes its shape - "1955. Under the placid veneer of suburban playparks and middle-class conformity churns a hidden London: femmes and butches dancing close in basement bars; clandestine love between women. To Sherlock Holmes, struggling private detective and mistress of disguise, it’s a realm she renounced years before. To Johnnie Watson, daredevil ambulance driver turned auto mechanic, it’s become a little too familiar. But when someone is murdered in the washroom of the city’s most notorious lesbian club, the investigation will lead both women to reconsider their assumptions about themselves, each other, and the world in which they live."