We’ve rounded the corner now and the kids are still loitering at the end of the street, kicking a rolling beer bottle to and fro across the road. A Border Patrol vehicle cruises slowly into view and a guard jumps out. The kids split and swerve round either side but the last one is too slow and, like a seasoned mountain lion picking off a baby goat, the officer pounces.

What happens next happens fast. The guard gets the boy down on his back, whacking him round the legs and letting loose a stream of ‘goddamns’ and ‘stinkin’ beaners’. Then a boot cracks into a rib and before I know it Duval’s over there.

He shoves the man hard. Taken by surprise, the guard loses his balance and drops to his knee, somehow managing to keep one arm pressed into the neck of the squirming child. His other hand scrabbles for his gun. ‘Fuck you . . . who the fuck?’ he splutters, but Duval doesn’t hesitate. He grabs the man’s arm and yanks it behind his back with such force that the gun flies out of his hand and slithers along the road towards me. Unexpectedly freed, the boy hightails it back to his friends, still jeering and screaming encouragement from the sidelines.

‘Beat it,’ Duval shouts, ‘all of you. ¡Lárguense! ¡Que se pierdan!’ And they scatter. I stare at the gun lying in front of me on the cobbled stones and feel scared, unsure whether to pick it up or kick it into the gutter. The border guard gets to his feet shakily and I think that’s the end of it, but it’s not. In his hand is a knife. He thrusts it towards Duval in a series of short chopping movements.

‘Back down,’ Duval says. In answer, the guard lunges once more, drawing his arm back and striking with a trajectory that for one terrible moment looks like it will end with the knife plunged into Duval’s neck, but Duval moves like a fighter. Quick, light, he sidesteps the blow effortlessly, and bringing his fist up to his shoulder he strikes the man once with the point of his elbow, and this time the guard goes down for good. For a frozen second no one moves. Not the guard, slumped on his belly, nor Duval bent over him. Then I sense something, some movement out of the corner of my eye, and I turn in time to see a car, headlights off, rolling slowly back-wards down the side street until it disappears from view.

‘You okay?’ Duval takes hold of my wrist and gently removes the gun from my hand, which is just as well as I am barely aware of having picked it up.

‘Duval . . .’ My heart pounds uneasily.

‘What?’

I glance again at the side street. ‘I think someone’s watching us.’

Duval narrows his eyes, but the road is empty, quiet. ‘Let’s go.’