The commotion was in the first street on the right after he crossed the Lungotevere de’ Cenci. In the half light of a single street lamp he could see a body lying on the ground, legs apart in a broken, unnatural fashion, the upper torso in darkness at the foot of a tall residential building.

Something was next to the figure, a pale shadow in what looked like child’s pyjamas, faint pink. This was the source of the keening, wailing scream that had brought him here.

He took out his phone, called the control room, identified himself and ordered an emergency medical crew.

‘We’ve had a call already,’ the operator told him. ‘Didn’t leave a name. Do you know what happened?’

‘No, but someone’s hurt.’

‘Need anything else?’

The figure in the pyjamas fluttered out into the light like a moth struggling to break free of a spider’s web. It was a girl, Costa thought immediately, and there was blood on her, on her chest, and in the loose, flapping fabric around her legs.

‘Make sure there’s some backup,’ he said, without quite knowing why. This was a complex, rambling part of town, on the very edge of the ghetto. There were people closing in, attracted by the noise. No blue flashing lights. Not a sign of a uniform, police or Carabinieri.

He was off duty, unprepared, a little heady from Falcone’s wine. But there was no one else around.

Crossing the street he called out, ‘Signora.’ Then looked more closely as he approached, saw her fully in the light, crying, distressed, quite beside herself, blood sticking in a messy smear across her slender chest and thighs.

‘Signorina,’ Costa corrected himself as he approached. ‘Police.’

He reached her, stopped, a little breathless. The girl was perhaps fifteen or sixteen. Her long blonde hair was the colour of old gold under the lamps and hung in thick tresses around her shoulders as she twisted and turned, trying to see what was around them, glancing anxiously at the shape on the ground. She had a beautiful, pale, northern European face, trapped between womanhood and the world of a child, innocent yet on the verge of knowledge.

There was a strange noise from somewhere nearby, like the trickle of water or sand.

‘Daddy,’ she mumbled in English, looking at the stricken body on the ground.

‘Signorina. .’ Costa took her skinny bare arms and held her. This was odd. There was still the sharp sense of danger somewhere close by. ‘Tell me what happened.’

She looked into his eyes and he found himself lost for a moment.

‘He fell,’ the girl said simply and glanced at the building behind them.

Costa looked at the figure on the black Roman cobblestones. After a decade in the force the rules came back without a second thought. Protect the living, protect yourself. Then, and only then, think of the dead. And this man was gone. He could see it, in the shattered skull, so broken he didn’t want to peer too closely, and the unnatural, agonized way the corpse was sprawled on the hard ground.

A handful of people were beginning to gather from the riverside road and the streets that entered from the ghetto. They grew quiet as they approached, encountering the invisible dread that came from meeting mortality out in the open, on a hot, idle August night. From somewhere came the sound of someone retching and he wondered whether the cause was the broken body on the paving stones or drink, or both.

The girl crouched down again, next to the dreadful shape. Her long, straight hair fell on the bloodied torso there. She kept mumbling one word over and over, in English, ‘Daddy, Daddy, Daddy. .’

It sounded wrong somehow. Too young a cry to leave the lips of a teenager.

Costa took in the way the dead man, a tall, skinny individual of late middle age he guessed, was leaking blood out into the cracks in the cobbles.

Around the body stood a pile of shattered rubble, old stone and cement. A few steps away lay a single piece of metal scaffolding and some planking. A thin trickle of pale dust was falling in a vertical line onto the ground next to what looked like fresh rubble close to the fathomless pool of darkness that was the entrance to the building behind them.

He looked up and saw the same beautiful, starry sky he’d been sharing with Agata Graziano only a few moments before. The man seemed to have fallen from an old, decrepit palace that stood a good five storeys high, one of the tallest on this side of the street. Against the moonlit night he could make out that the top floor had a balcony running the width of the building, with scaffolding attached for part of its length, suspended on cables that led to some apparatus on the roof. The nearest corner, almost directly above them, was gone entirely, both metal railings and terrace ripped away, leaving a line of broken tubing, cracked concrete and ragged wire clinging to the stone facade.

The contraption was moving perceptibly in the darkness.

The steady trickle of fragments of stone and sand grew stronger, depositing a growing pile of rubble on the ground.

Four years before he’d been called to a tenement in Testaccio rented to illegal immigrants, the clandestini who performed the jobs that Romans had come to believe were beneath them. The building had been denied maintenance for years, against the city statutes. On one grim December day an entire wall had collapsed, burying those unlucky enough to be inside. He’d never forget clawing at the rubble to get to a child, or the relief he’d felt when he was able to retrieve a single young soul from that bloody, choking mess.

His head cleared very quickly as he turned on the growing crowd of bystanders, many of them foreign, some of them drunk, and yelled, ‘Police! Get back! This is a building collapse. Clear the area. Now!’