But not tonight. As the blinking lights of Phoenix airport appear below like a defiant grid of life on an inhospitable planet, I feel a surge of adrenalin. Tonight will be different. Tonight there is no turning back. In about an hour’s time we will be at the head of the immigration queue. Poised for entry. The customs official will give me and the children no more than a cursory once-over before stamping our visa forms.

‘What is the purpose of your visit?’ he will ask.

The pickup truck has a side-swinging motion that the Mexican corrects every few seconds, bringing it back into line on the right side of the road. Every time my eyes begin to close with the rhythm, the wrench of the wheel forces them apart again. Right now I’d give anything to slip between clean sheets, sleep until it’s time to let tomorrow begin, but the silence in the truck feels reproachful. No doubt the Mexican is pissed off at having to pick us up – well, too bad. Quite apart from the fact that I would have killed the three of us falling asleep at the wheel, the town is so remote I would never have found my way there in the first place.

I study his profile surreptitiously. He is more Spanish-looking than I remember – though it wasn’t until we cleared customs that I experienced a moment of panic: what on earth did he look like? What if I didn’t recognize him? What if he didn’t remember me? What if he didn’t show up at all? I’d held a vague picture in my head over the last few months of a shortish middle-aged man with tightly curled hair greying at the edges and a brushstroke of a moustache, but the truth is, all I could be really sure of was that he looked, well . . . Mexican, and at Phoenix airport, as it turned out, that wouldn’t exactly have made him stand out from the crowd.