Diverted to Victorian London by persons or powers unknown, twenty seventh century archaeologist, adventuress and inadvertent absent mother Bernice Summerfield finds herself beset with problems of a kind that those unused to time-travel could barely even imagine. What are the plans of the mysterious Lord Straxus? Who is Ludvig Cooray and what has the number seven to do with all this? Can Bernice acquire the help of Mycroft Holmes, the cleverest man of the age, and more importantly how is she going to get home?