He was about twelve, as I remember. His face was beautiful and serene, quite feminine in its delicacy, with traces of gold paint glinting on the nose and cheeks, and with a bit of red ribbon tied in his damp brown curls. His throat had been cut. His body had been slashed open all the way down to the groin and emptied of its organs. There was no blood, only that dark, elongated cavity, like a gutted fish, filled with river mud. How Cicero managed to contemplate the sight and maintain his composure, I do not know, but he swallowed hard and kept on looking. Eventually he said hoarsely, 'This is an outrage.'

'And that's not all,' said Octavius. He squatted on his haunches, took hold of the lad's skull between his hands and turned it to the left. As the head moved, the gaping wound in the neck opened and closed obscenely, as if it were a second mouth trying to whisper a warning to us. Octavius seemed entirely indifferent to this, but then of course he was a military man and no doubt used to such sights. He pulled back the hair to reveal a deep indentation just above the boy's right ear, and pressed his thumb into it. 'Do you see? It looks as if he was felled from behind. I'd say by a hammer.'

'His face painted. His hair beribboned. Felled from behind by a hammer,' repeated Cicero, his words slowing as he realised where his logic was leading him. 'Then his throat cut. And finally his body… eviscerated.'

'Exactly,' said Octavius. 'His killers must have wanted to inspect his entrails. He was a sacrifice – a human sacrifice.'

At those words, in that cold, dim place, the hairs on the nape of my neck stirred and spiked, and I knew myself to be in the presence of Evil – Evil as a palpable force, as potent as lightning.