When Scarlet's grandma goes into a retirement home, she must sort through her belongings in the cramped flat above a shop in Crouch End, north London. Here Scarlet comes across a real treasure: a novel that Gran wrote, imagining the life of a girl just like Scarlet, who once upon a time lived in the flat and worked in a cake shop downstairs. But as Scarlet reads about Ruby's life in Victorian London, she begins to realise this is no piece of fiction - Ruby was real! A real life, facing real danger - and a mystery that unravels to the present day.