Joan's house was in Guildford. It was a small place—red brick, mid-terrace, with a narrow garden at the back that was more pave than lawn and a front door that opened directly onto the street. From the outside it looked like any other house on the road: ordinary, unremarkable, the kind of house you walked past a thousand times without noticing. But inside it was different. Inside it was warm and cluttered and alive with the evidence of a mind that could not stop working—books stacked on every s...