Down here in the grave clay, all the buried energies that feed the overworld are pooled. This is the ghost sump. Apparitions, sewer dredgers drowned by sudden flood, rat spectres, subway phantoms. Tomb talk, in the hollow black.

Beneath Holloway Road, one of the city's subterranean rivers rises from two springs, two heads better than one. The Hackney Brook, dual currents plaited in a cold chrome braid, underworld Perrier. A twin tide, heading east.

A dead man's flue, the under-river will discharge its secret metals, its contaminants, into the River Lea.

Down here, in the exchange of salt and sand, fluid intelligences meet in prehistoric conversation, methane dialogues.

In 1859 Joseph Bazalgette, now a bronze head near Hungerford Bridge, engineers interceptory sewers, voiding London's wastes into the Thames, one pig-iron colon winding under Highbury Hill to swallow Hackney Brook in giant acoustics.

Underage toshers trawl the human silt for coins, for lost engagement rings—prospectors up shit creek, panning for diamonds, like the rest of us. But then the waters rise. The sewer portcullis of the penstock chamber slams down, loud and final.

In 1963, construction starts on the Victoria line. Immense drum-diggers with rotating teeth, injected liquid nitrogen to freeze the water-bearing gravel. Science fiction hardware chews its way across the city, coughing sparks.

The work unearths six fossil nautiloids, each sixty million years old, near Victoria; ploughs through a plague pit at Green Park. Further along its six-year crawl, at Highbury, it meets Bazalgette's sewer. Nightworks are entailed. Curfew machinery.

1913. During foundation work at Highbury stadium, locals are invited to contribute backfill. One, a coalman, gives more than intended when his horse falls in, poleaxed and buried on the spot. A bone mare, rattling loose beneath the Arsenal ground.

Beneath the seated and sedated stands it lopes along the clay bed at a graveyard canter, nothing holding it together but a cartilage of mystery, its funeral hoofbeat ringing in Bazalgette's sewer bore, kicking up sparks on the Victoria line.

A skeleton horse!

It will be ridden by Epona, underworld horse-goddess, worshipped by glum Gallic cavalrymen at Rome's Highbury garrison. Holding her iron key to Death's bible door, she'll ride down Hackney Brook, sidesaddle on a corpse, her skeleton horse.

The earth closes about us. Veined with wire, pipe-boned, a filthy subtext. Marsh gas flares in rusted catacombs. Move up, between the shale drifts, to the streetlamp follicles, eye-level Highbury rising from black earth into another element. The flood of animal emotions surging in the street. Present desires precipitated. Curdled to a sea foam.