I make my way cautiously down the steps, the bright oblong from the hatch above me lighting my way, wondering how long it took Dad and Kemp to do the same. The steps are wide and even: Victorian engineering. It’s dusty and fusty and there’s that chalky, brick-y damp smell, the one that is neither pleasant nor unpleasant. I feel nervous, slowly descending these concrete steps, leaving the world above me and entering the unknown. I reach the platform, hesitate; I continue down. When I get to the last step I can’t help but gasp, because in the ghostly light filtered from the hatch I can see exactly why Dad wanted to come down here.

Before me is a high-ceilinged domed tunnel of dulled-amber brick arches stretching endlessly, like an Escher drawing, into eventual blackness; a curved concave brick threshold at the base of each, rising at either side to form a row of disappearing sentry pillars, between which are an infinite series of curved eyelets in the brickwork – more arches, more tunnels – extending into the distance, with ever-decreasing centres, like wombs. The reservoir is the size of a football pitch, according to Dad. It’s like being in an ancient golden-hued subterranean cathedral, with no idea of where it ends or begins. I can see why it has been used as a film location. It’s stunning.

I call, ‘Dad? Kemp?’

There is standing water between each arch – a limpid black pool in a repeat pattern as far as the eye can see. I’m going to get my feet wet if I go any further, but I have to go further, don’t I? They must be in here.

I set off into the first dark pool of water, muttering amalgamated swear words under my breath. I’m wearing flip-flops; I changed into them back at The Palladian as my sandals were beginning to rub. They squelch and sluice up great swathes of water with each step, so I take them off and put them in the back pockets of my turned-up jeans. The brickwork at the bottom is smooth underfoot. I can feel the mortar joints, the slight indentations between bricks under my toes. I walk. I walk through two or three arches, sloshing through the water that is calf deep, and cool but not cold, and stepping over each brick threshold. I try not to think of the park above me, suspended above this domed ceiling of amber. Of the two boys up there. Of the fairground. Of Salvi.

When I reach the next threshold, I call again.

‘Dad?’