For a heartbeat all was still. Audax and Constantine were locked together, the knife hilt still in the slave’s hand, the blade in the Emperor’s chest. Constantine’s mouth gaped, with strings of spittle stretched between his lips. Audax’s hand felt small, pressed against the huge warmth of the Emperor’s body.

Then there was pandemonium. Helena screamed, the soldiers yelled and drew their weapons, and Thalius and Aurelia were both grabbed and held. But nobody dared touch the Emperor himself, or the boy.

Constantine raised his hand, and everything stopped.

The Emperor was breathing slowly, carefully, and he kept his eyes locked on Audax. ‘Don’t move,’ he said in Brigantian.

Audax was surprised enough to speak. ‘You know Brigantian.’

Perhaps his arm moved, just a tiny bit, as he spoke. Constantine gasped, and his huge body shuddered, as if he was a puppet controlled by the boy, and the knife.

Constantine said breathlessly, ‘I was a soldier here, serving under my father, for many years. This was my home. I learned British. What is your name? Nobody thought to tell me.’

‘Audax, sir.’

‘Audax. All right, Audax, listen to me carefully. There are two very important things that I must tell you. The first is that I know that it wasn’t your fault. I saw the woman push you - what is her name?’

‘Aurelia.’

‘Yes. I saw it. So whatever happens today, if I live or die, you won’t be punished. Do you believe me?’

Audax thought it over. ‘No,’ he said.

Constantine gritted his teeth. ‘I wish my advisors were half as honest. I am the Emperor, Audax. If I make a promise it is kept. So believe me.’

‘What is the second important thing?’

‘The second thing is that as a soldier I learned a lot about the human body. Mostly by cutting holes in other people. And I know that if you move that knife, even a little bit, you will puncture the vessels of my heart and I will surely die. If you do not move it, I might yet live. Do you understand now why I asked you to stand still?’

‘Yes,’ said Audax.

Yes, he understood. But his arm, held out straight, was tiring, and the blood was seeping out of the Emperor’s robes, bright crimson, and soaking his hand in slippery warmth. He did move, just minutely, no matter how hard he tried to keep still. He couldn’t help it. And with every jerky motion he felt the Emperor shudder and twist in response. It was the way Audax had seen crucified slaves jerk and twitch, tiny motions as they tried to relieve the pain in their chests and feet. And just as Audax had learned to recognise mortal fear in the faces of the crucified, so he saw fear on Constantine’s greying face now, beneath the clamp of calm.