No one else says anything and the heavy moment passes. I lean forward in my seat, staring intently as we approach Old Tucson. I hold my breath and glance around fearfully, worried that this will be a weak point in the defences, but we pass easily through a heavily armed gate, moved for the purpose of our small envoy. Diogo lifts a hand to the men guarding the checkpoint. They nod and return to duty once they've pushed the heavy gate topped with barbed wire back into place.

I ...