Even as I say it, though, it occurs to me I don’t have one myself. Frankly, I’d never given border crossings much more than a second’s thought until this evening. Besides, nowadays it seems like the whole world is on the move. Hideaways, stowaways, refugees, asylum seekers. The terrible images wash over you until you don’t even notice them any more: cities of camps built on slivers of boundaries between countries populated by misery. Sangatte, the Channel Tunnel. Destination UK.

Before first coming to Arizona, if I was ever to think about Mexico, it would be to conjure up images of mariachis in silver-threaded sombreros crooning mournful love songs, villains with pebbledash complexions blowing curling smoke from the top of guns, crosses atop churches in white sun-baked towns or braided virginal beauties fleeing banditos through verdant fields of tequila. Mine was the clichéd Mexico of Hollywood’s hard-bitten romances: The Magnificent Seven, A Touch of Evil. Then I saw a movie, Men with Guns, in which a professor at a medical university in Mexico City dispatches a bunch of his best students, all filled with the milk of human kindness, into the poor rural communities in the Chiapas region. When they disappear he sets out to find them. His search takes him to sugar-cane plantations and tiny towns in the mountains, lost and forgotten communities where he is met with a world of oppression and hostility. It turns out that all his students had been murdered, the only woman doctor amongst them raped and crucified first.

Nevertheless Mexico looms invitingly on the other side of my mountains, a country to be dipped in and out of at will, but although I’ve a powerful curiosity to explore it, I’ve not yet done so, still awaiting I suppose some psychological visa that will allow me to embark on the great untapped adventure I know it represents.

Duval still hasn’t answered.

‘Come on, Duval.’

‘Doesn’t matter what I think,’ he says finally.

‘Why not?’

‘Because it’s not my problem and it’s not yours either.’ He stops the truck at the turn-off to Temerosa. ‘Listen to me, Alice,’ he says roughly. ‘I don’t know what it is you’ve come looking for, but whatever it is, don’t count on finding it out here.’

I look into his face, but it’s impossible to read anything in those dark eyes. It should make me angry, this second veiled warning of his, but it doesn’t. I just feel triumphant that after all this time he’s finally called me by my first name.

Benjamín has got the children into bed and asleep by the time we reach the cabin. I find him sitting in the corridor upstairs, where he has stationed a chair outside their room like a White House security guard in charge of high-risk diplomats.

‘I’m sorry, Benjamín’, I whisper. ‘It’s so late.’