The idea came, like many good things, from a trip to the pub. My sister and I had taken a slow autumn walk by the Thames. We ambled east through Southwark and Wapping, arriving at the Prospect of Whitby for a late lunch. A sign above the bar explained that the building’s structure came from the carcasses of ships, including the pewter-topped bar, masts and barrels buried in its walls. Pirates and vagabonds once gambled at the narrow tables, when it was known as The Devil’s Tavern, back in 1520. I stared through the window at Execution Dock, with its yardarm still intact. Peter Ackroyd’s description of the Thames as the ‘river of the dead’ had never seemed more accurate. It was easy to imagine a modern day killer becoming so obsessed by the river’s dark history, he might hear it calling to him, begging for more souls. After all, murderers have drowned their victims in its depths since long before the days of Jack the Ripper.

I returned to the embankment often as my characters came to life. Solitary walks at dawn revealed the river’s brute power, as well as the rubbish it’s been forced to swallow, from rusting beer cans to prams and bicycles. I discovered that the black silt of the Thames has a particular smell: boat diesel, effluent, and rotting fruit. My wanderings took me to deserted docks and piers far from the public eye, where a killer could watch his victims drown in privacy.

The Museum of London turned out to be a brilliant resource. It was packed with artefacts dredged from the Thames, including Bronze Age daggers, thousand year old glassware, and Roman jewellery. I learned that the river had served as a burial ground for centuries. Hundreds of skulls were revealed by a dredger at Vauxhall Cross, proving that Bronze Age warriors had cast their victims into the water. The Romans too had made offerings, to honour their dead. Since the earliest days of settlement people believed that the vengeful power of the Thames could be pacified with tributes. Like ancient Londoners the killer in my book believes that his safety can only be preserved by making human sacrifices to the city’s vast waterway.

The 213 mile long river remains a popular place for the disposal of bodies. On average one corpse per week is found in the river. Vicious currents and freezing cold temperatures mean that anyone unlucky enough to fall in alive in winter will only survive for two minutes. Countless human remains have been found in the Thames, from the Kray brothers’ gangland victims to the present day. One of the cases that touched me most was that of Zoe Parker, whose body was found between moored barges at Battersea in December 2000. The young sex worker was so alone in the world that no one reported her missing; after months of investigation she was identified by her tattoos, but fifteen years later no one can explain her violent death. Such emotive cases made me wonder why a murderer would discard his victims’ bodies in the river, as if such terrible deeds could be washed clean.

Writing RIVER OF SOULS gave me a taste of the Thames’s potency as an artery for the city’s freight, but also as a repository for countless human souls. As the final draft of my book took shape I realised that I couldn’t write about it with conviction until I’d experienced the water myself. So on a chilly March day I slipped off my boots, rolled up my jeans and stepped into the water at low tide, below Blackfriar’s Bridge. The silt slipped beneath my feet, the water breathtakingly cold. Currents tugged at me, even in the shallows, as if the river wanted me for its own. Fascinated as I am, I’ve never been happier to scramble back onto dry land.

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Kate Rhodes has written two prize-winning collections of poetry and four crime novels. She is currently completing the fifth novel in her Alice Quentin series, featuring the work of a London-based forensic psychologist. She was born in London but now lives in Cambridge with her husband Dave, who pretends to potter about aimlessly, but also produces short stories, plays, and animated films.

River of Souls is Kate’s latest novel.