A bonfire that moved. A blinding column of fire that surged nearly seven feet high and twisted and jumped and shook. A bonfire that screamed. And then the screams became words. Words that I didn’t understand, although the agony behind them was unmistakable. Instinct kicked in. I opened my mouth to yell at the others, to tell them to get him on the ground. I was starting to take off my coat, meaning to wrap it round the man who was the bonfire, roll him up, get water from somewhere, and as I did so the realization dawned that this was no band of horrified onlookers. The figures surrounding the burning man were too still. They watched, their bodies showing no horror, no panic. Each carried a rough stick, a broken branch, which they held out before them, as though to ward off the staggering, dying figure if he came too close. Each wore a grotesque, carnival-style mask.

It was coming at me. The human bonfire had seen me, was running towards me. I could see eyes, arms reaching out, the screaming was aimed at me now. The others had seen me too. Three, four, five dark figures had turned my way. I saw wolf’s teeth, a green, bug-eyed alien, the cracked skin and staring eyes of a zombie, a goblin with a tight leather skullcap, and, strangely, the most horrifying of all, a tiara-wearing Queen. All coming towards me.

‘Police!’ My warrant card was held high. Not that any of them could see; it was far too dark. ‘Stay where you are!’

They didn’t, of course. Thank God. They ran. I’d like to think it was the authority in my voice that drove them away, but far more likely they heard the approaching siren before I did. One yelled a command and turned. The others followed. There was only one way into the park and I was standing there, but they pushed their way through bushes and I could hear them scrabbling over the railings. On the other side were football pitches edged in a narrow strip of woodland, a large area of open space.

They say that people commended for acts of courage talk afterwards about not thinking, just acting. I certainly didn’t think that night, although there was no talk of courage afterwards. I ran towards the burning figure, by this stage prone on the ground. He was still burning and the acrid smell of petrol, smoke and scorched meat was sickening.

I say ‘he’ and ‘him’. At this stage I had no idea.

I pulled off my coat and flung it over him, covering his head, dropping to the ground, picking the coat up, putting it down again. The coat was long – nearly ankle-length on me – and made from heavy red wool, but the flames weren’t giving up easily.

They told me later that he didn’t burn for too long. That it was lucky I lived so close and was familiar with the layout of the park. Someone else might not have known where the Parks Department kept their water-hose, or how to bypass the locking device that prevents unauthorized use.

Nothing about it felt lucky at the time.

My coat was starting to smoulder. I gave up on it and ran instead for the hose as the sirens drew closer. It took much longer than I’d have liked to unravel it and turn it on, and when I got back he was still on fire. The flames gave way quickly to the water, though, and were out in seconds. I carried on hosing him down, knowing that cold water is the best immediate treatment for burns, until it occurred to me that I might actually be drowning him.

‘DC Flint in Larkhill Park, Kennington, requesting urgent assistance. One casualty. Possible fatality. Ambulance needed. Very serious burns.’

The last was an assumption on my part. A reasonable one, in the circumstances, but I could see very little.

‘Five suspects running in a westerly direction across the park towards the Wandsworth Road,’ I went on. ‘Casualty believed to be male.’ I’d seen the size of the feet sticking out from beneath my coat, the masculine-looking shoes. And he was tall. Not far short of six foot.

People were coming. I could hear voices, running footsteps. A uniformed female constable appeared at the gates, followed by an older, heavier male. They took in the figure at my feet and stopped dead.

I don’t remember much about the next half-hour – just more and more people arriving. Onlookers and rubberneckers at first, driven by macabre curiosity and easy to contain. But more and more came, outnumbering the police, giving me no choice but to pitch in and help. One quick-thinking copper gave me his high-vis jacket so it was a bit clearer which side I was on.

The railings around the park should have helped, and for a while they did. We kept the crowd on the other side of the gate and they were content to watch from a distance. But as the crowd got bigger, those at the back couldn’t see, and those with a little more courage (or a little less human decency) started to scale the railings and creep closer. We had to spread out, forming a circle around the figure. The female constable who’d arrived first and her partner were kneeling by the body, trying to administer some immediate first aid, and I was massively grateful. I couldn’t have done it.

Curiosity inevitably gave way to unrest. Few people like being told what to do by the police, and soon the crowd started to shout angrily. Accusations flew like sparks. A middle-aged man in traditional Muslim clothes, with black hair and dark skin, pushed his way to the front of the crowd, yelling about his son. Where was his son? Someone had hurt his son, let him through, he had to get to his son. More men appeared, some the same age as the first, some younger, then a few hijab-clad women, their brown eyes bewildered and scared.

Arguments began to break out. Everyone wanted to get closer to the body. No one wanted to go home. Someone stood on my foot, someone else elbowed me hard in the face, and all the while, heavily accented voices were shouting about someone’s son, someone’s brother and why couldn’t the fuckin’ pigs let them through.

While they did so, the man lay on the ground, horribly injured, possibly dead.

The uniformed sergeant in charge did his best, but it was an impossible situation. The ambulance arrived and the crowd, to give them their due, allowed the paramedics through unscathed, but then surged forward again as the police barrier began to weaken.

The sergeant went down. A constable who stooped to help him was knocked off his feet. We’d lost control. It happens so quickly in crowds: one second everything’s in hand, the next all hell is breaking loose and all you can really do is run for it and regroup. People often ask the police, are you ever afraid? I was afraid that night, in the midst of a crowd that was quickly becoming a mob.

As the police cordon broke, the man who’d been yelling for his son ran forward. Others followed – there was a small woman, with a long scarf over her head, and one of the men put an arm around her as they hurried forward. The sergeant, back on his feet and with one arm raised high in a surrender gesture, held on to the first man’s shoulder. ‘Stand back, sir,’ he tried. ‘Let the paramedics do their job.’ He was pushed away. The man knelt down by the injured body. I didn’t see what he saw. I imagine few people did. We were mostly too far away and the light was too poor. It made no difference. What we heard told us everything.

Screaming. Keening. Yelling. I honestly hadn’t known human beings could make such a sound. It was the sound of agony.

‘OK, come on, get ’em back. Everybody back.’

Someone was trying to take charge again. We forced ourselves to muster, to link arms, to face the furious crowd and do the ‘Step back, sir … Everybody back now … Give us some room’ thing. A police van arrived and from its rear doors spewed officers in riot gear. The pictures in front of me began to merge. Sharp torch-beams, the lurid Day-Glo of police uniforms, shouting faces, accusing fists, a crowd still angry but growing colder and calmer. I saw very little of it. The only clear image in my head was that of an elderly Muslim woman on her knees in the mud, tearing her scarf and her hair as she howled at the moon.