‘This is the police,’ said a voice above, an amplified recording. ‘Disperse immediately.’

The drone’s lights swept the clearing, ending their dazzling focus on me and letting me get a good look at the machine: four fat rotors clover-leafed around a hub of cameras and lights, the blue badge of the Metropolitan Police transferred on its white and yellow hull.

‘Disperse immediately,’ the drone repeated, and the youths needed no further invitation – they scattered like birds at a gunshot.

Pierce did not budge. He lay exactly where he had slumped after tumbling off me. His hand was still clasped around the handle of the knife, the blade of which was lost inside his chest. He stared into the open night sky, not looking at the drone or the widening smoke from the wreck of the car, not looking at anything.

‘Disperse immediately,’ the drone repeated in its curt recorded voice. It spoke only to me, and I listened.

I did not go back the way I had come in. I did not fancy returning by the meandering path we had followed from the main entrance, especially if there was any risk that the youths had paused in their flight upon reaching the street – or worse, were being held there by the police. Besides, the nearest gate lay to the north, at the end of a wide, straight path.

Once I was out of the cemetery, I had a clear view along an alley that followed its wall towards the entrance corner, and no blue lights were congregated there, or hooded figures. The smoke from the car was weakening as the blaze burned itself out, and by the time I reached the main road it could no longer be seen. A fire engine streaked past, sirens shrieking, turning towards the park.

There had been no fraud. Night Traffic was the truth, and Pierce’s confession was the lie. I had understood as soon as Pierce had recognised our assailants in the cemetery – our would-be assailants. All the inconsistencies in his account had evaporated at once, and all his evasions had been explained. Quin had uncovered no evidence of deception because there was nothing to uncover; Pierce could not commit to giving details of what he had done, because he had not done it.

Why, then, had Pierce been moved to confess to a crime that he had not committed? To a crime that had not been committed?

I imagined Pierce in his hermitage, and the bright boys and girls of Bunk arriving, sifting his papers, turning up the notes he had made in the distraught days after the attack. He had not feared discovery of a lie – he had feared facing the truth.

The attack described in Night Traffic had been real, and so the intense trauma he described there had also been real. He had told how he turned to writing in order to cope with that trauma. But he had gone further. He had convinced himself that by turning the attack into writing, he had turned it into fiction, that his description was his invention. He wanted it gone from memory, so he smoothed it into the realm of inspiration.