In every major town and city, there is a house of which no official record exists, and whose windows have been boarded up for longer than anyone around can remember. The previous occupants, if there ever were any, are untraceable, and no organisation or individual will ever lay claim to the plot on which it stands.

Nevertheless, when you break in–always through a back, ground-floor window; you must never touch the outer doors–you will see amongst the dust the signs of inhabitants long gone. A flattened cardboard box, an overturned child’s cot, balding patches on the carpet where the pile has been worn away. Invariably there will be an orphaned double mattress in the master...