Standing in a fug of heat outside Cairo airport, taxi drivers shouting at me, night falling fast and without a single coherent idea about what I am to do, I stare into space, resisting the urge to turn around and buy a one-way ticket back to Heathrow. I have left England only once before, on a school trip. In my pocket I have £300 and the Nairobi address of a distant relative I’ve never met. This is supposed to be my great African adventure. It doesn’t feel that way.