Because of the crazy driverless lorries, the pavements are no longer safe, and we are forced to walk along high ledges, parapets and rooves.
My shadowy partner is more fit than me jumping up athletically; I just can't do it.
We decide the other option is to travel through the city basements avoiding danger that way. A special booklet is provided which is like a kind of basement passport.
I don't think it will work - I am sure no-one will know what it is.