People started to shout, hurtling in every direction. I froze as the ground seemed to tilt. The drone of voices became a chain-saw scream. Many screams. Something struck me in the stomach, a fist or boot. I doubled over, gagging, finally looked up again.

The demonstration had exploded into a riot. Everywhere people ran, or tried to, pushing others to the ground and trampling them as lines of helmeted figures, black and neon green, raced from behind the monument, wielding riot shields. A man shrieked, a child’s thin wail grew abruptly silent as a woman screamed. I stumbled backward, turning to flee in another direction.

But there was no other direction, no up or down or left or right; only a heaving ocean of limbs and faces.

The crank’s quicksilver halo fragmented into a world like a damaged negative, eyes, mouths, faces all obliterated. The ground seemed to shiver, as though a huge hive hummed furiously beneath my feet. Blurred hands, gaping mouths, a thicket of jerking knees and feet and the stink of vomit. It was like falling into hell’s own mosh pit. I choked, tasting blood where I’d bitten my lip. Snatches of robotic-sounding speech echoed as a helicopter circled overhead, its rotors sending up waves of grit and mud.

If they start kettling, get the hell out.

I pressed my bag against my face, in case someone lobbed a tear gas canister; kept my head down and zigzagged through the mob. Not far away, a woman with a Union Jack painted on her face screamed obscenities at a cop. Beside her, a heavyset man swung a DOA sign like a battle-ax. A mounted policeman wheeled and galloped toward him, people fleeing from the horse as though it were a tank. My inchoate terror dissolved into a more practical fear: not of tear gas but getting arrested.

I lurched toward a break in the crowd, finally halting in a patch of grass. Gasping, I lowered my bag. The crowd was sparser here, mostly people like myself struggling to catch their breath. A few onlookers ran toward the melee, mobiles held up to record the event. Four old black women followed them with arms linked, their hair hidden beneath brightly colored turbans. A loudspeaker blared a warning as sirens sounded in the distance.

A few yards off stood a man, short, white, bald, in a faded green parka with ratty fake-fur trim. A laminated card hung from a lanyard around his neck. He held an SLR camera, its lens pointed to where an arm punched upward through the crowd, wielding a police baton. The baton fell, and I heard a thump, then more screams. The photographer had barely lowered his camera when someone lunged at him—another cop with a baton.

I watched as the crank sizzled in my brain and everything around me began to slow. The photographer’s mouth gaped wider and wider as he fell, but no sound came out. His hands opened and the camera floated into the air, as though he’d released a black bird.

With dreamy slowness, the photographer rolled onto his side. The policeman loomed above him, baton raised. The camera dropped onto the grass a few feet from where I stood, its lens pointed skyward. The photographer covered his head with his arms as the baton came down on his skull with a dull crack.

Someone shouted. The four old women stopped to look back, then with shrill voices raced toward the cop. As they surrounded him, I snatched up the camera and darted through the crowd, which had begun to scatter. It was a long time before I slowed to a walk and glanced behind me for signs of pursuit.

No one appeared to have taken any notice of me. The demonstration had broken up so swiftly that it scarcely seemed as though it had ever happened. The Nazis in their distinctive white shirts and brown pants were gone, along with almost everyone else. A pair of mounted police officers made slow figure eights around the monument, circling those who remained, like cowboys rounding up cattle. Onlookers stood at a safe distance, along with several TV crews, recording the riot’s aftermath on mobiles and videocams.

Two police helicopters hovered above the monument as a police van drove across the grass, lights flashing, and stopped near a group of policemen who stood in a half circle, staring at something on the ground. A woman hopped out of the van, followed by two white-suited figures, and all three walked to join the others.

Out of nowhere, a small black shape appeared and swooped above them, low enough that the woman looked up in alarm. Another drone, I thought; then saw it was a bird, a crow or raven that abruptly banked and headed in my direction before veering off into the trees, where I lost sight of it.