The Thames is clean again. For Tom Kean, co-founder of the Henley Swim, it’s the availability of cheap, effective wetsuits. For Davies — a novice swimmer, she admits — it’s a quest to immerse ourselves in wild nature. She writes much more quickly than she swims — and the chapters detailing her own experiences wriggle with more ‘I’s than eels in the newly clean river — but she’s an excellent listener. The conversation that lingers is on board a Port of London Authority vessel: that little wooden hut on a pier at Wapping is a mortuary where 30 drowned bodies are examined each year. In the 1870s it was five times as many but what hasn’t changed is the nature of the river itself. You’ll bob up three times, and your corpse won’t float.