One afternoon in July 2011, an 11-year-old boy named William Knowlden was out cycling with friends when he came upon Arnolds Field, an expanse of green land in Havering, east London. The site spans about 17 hectares, or 24 football pitches, and around its perimeter runs a wooden fence, with two access points through which vehicles can pass. Arnolds Field rises much higher than the surrounding land. Its surface is lumpy and undulating, like a blanket thrown over a heap of cuddly toys. The land is overgrown. It has been decades since animals grazed there, and few people have set foot on it in recent years. But every so often, it is mistaken for a safe place to explore.

As Knowlden descended a hill, he lost control and was thrown over the handlebars. When he came to, he was lying in a small crater and his feet were covered in a powdery residue that resembled ash. He felt a sharp pain in his left foot. When Knowlden’s friends arrived, they removed his shoes and peeled back his socks. One foot was pink and swollen, the skin blistered and shiny; the other was blackened and charred. Patches of skin hung off, revealing layers of fatty tissue. “It looked like it had been eaten by maggots,” Knowlden recalled. “Like pure, pure flesh.” In hospital, doctors informed Knowlden that he’d suffered third-degree burns in his right foot. They were baffled. With thermal burns, there should be an identifiable source of heat, like an open flame, but Knowlden and his friends hadn’t seen anything like that.

In the years following William’s accident, his mother, Nicola, became fearful that there might be something seriously wrong with Arnolds Field. Smoke would occasionally rise up from it, and a strange smell, like burning plastic or rubber, would engulf the neighbourhood. “I was like, ‘Oh my God. What on earth is over there?’” she told me. She wasn’t alone. Around 2014, fishers at a lake next to Arnolds Field became suspicious when the fish started mysteriously dying off. One local woman, Barbara Thwaites, told me that around this time, she had started to have respiratory problems. When her husband suffered severe respiratory collapse and died, she grew even more suspicious. “I knew something was going on there, but I didn’t know what,” she told me. After her son’s accident, Nicola Knowlden says she wrote an email to the council, urging them to investigate, but never heard back. (Havering council says it has no record of this email.)