Never once, she proudly informed me, had she reminded the boy of his mother.

I smiled thinly and assured her that Agrippina would never forget such a remark. I also called on Uncle Claudius in the library of the Senate house. His twisted face was unshaven, his tunic and toga soiled with dust and ink. He walked me up and down the rows of shelves, dragging his foot behind him, whilst delivering a lecture on the possible ancestors of the Divine Augustus. Round and round we went until I became dizzy. In a shadowy, dusty corner, he abruptly paused and sat down on a stool, mopping his face with the rag he kept up his sleeve.

‘Are you part of it?’ he asked. His eyes had lost that empty, vacuous look. His mouth was no longer slack, the jaw line seemed firmer, his voice free of any impediment. He spoke clearly and distinctly whilst those shrewd grey-green eyes studied me.

‘So, you are Agrippina’s man?’ he asked.

‘I am.’

He puckered his lower lip. ‘And are you one of them?’ he repeated.

‘One of what, sir?’ I asked.

‘You know full well,’ he teased. ‘Caligula is going to die, isn’t he? He’s obscene. He’s mad and his wickedness grows every day. At the moment, he’s absorbed in his games but soon he’ll lash out once more and his kin will feel his wrath. The signs are all there. The portents. .’

‘What portents, sir?’

Claudius sighed. ‘The Capitol has been struck by lightning,’ he explained. ‘As has the Palatine here in Rome. Sulla the soothsayer sent a message to the Emperor to be careful.’ Claudius’s eyes narrowed. ‘Caligula has been told to beware of a man called Cassius. But we don’t need the Gods, do we, Parmenon, to tell us there’s going to be a change?’ He made a rude sound with his lips. ‘Oh, don’t worry, we can relax here. Spies find it very difficult to listen to conversations in a library, they can’t openly eavesdrop; it’s the best place to plot a coup. Come on, man, are you part of it or not?’

‘Yes, sir, I am.’

Claudius rearranged his cloak round his shoulders.

‘Now listen carefully, young man. Agrippina is directing matters.’ He laughed at my surprise. ‘Oh, didn’t you know she’s been writing to me? Don’t be offended,’ he soothed. ‘Agrippina wouldn’t tell you lest you were captured and tortured. She wouldn’t use you as a messenger for the same reason. Caligula is to be killed and the best chance is as he leaves the games or the theatre. If we can separate him from his guards, the others will fulfil their task.’ He tapped his sandalled foot on the floor like a schoolmaster giving instruction. ‘Cassius Chaerea is a leading conspirator. Caligula still heaps insults on him: last night he made him kiss his little finger then waggled it in a most obscene manner. My only fear is that Chaerea may not be able to contain himself and strike before we are ready.’

‘Will you be involved?’ I taunted.

In answer Claudius got up and stood with his fingers to his lips as he examined scrolls on a shelf. He murmured to himself and plucked one down, greasy and stained with age.

‘Do you know what this is, Parmenon? It’s an account of Julius Caesar’s assassination. All those involved in his murder died violently themselves. I will not suffer a similar fate. I will act the frightened rabbit, and I suggest you do likewise. If, and when, the blow is struck, distance yourself. Ensure that the young Nero is safe and sound, and that I — ’ he smiled ‘- am discovered cowering in some apartment in the palace. If that’s done, all will be well. The rest,’ he spread his hands, ‘is in the lap of the Gods. Now, I’ve got manuscripts to file and you’ve murder to plot.’

He rose and shuffled away. I suppose with someone like Agrippina you learn something new every day. I had always regarded Claudius as a fool, but Agrippina thought otherwise. She had learnt her lesson and, like Uncle Claudius, would not show her hand. Cassius Chaerea was different: his hatred for the Emperor was now a consuming passion. After nightfall, when free of the Emperor’s spies, we met the other conspirators out in the gardens or shady groves where Cassius’s men could defend us. Other tribunes of the Praetorian Guard were drawn in: Papinius, Asiaticus, Clovinus Rufus an ex-consul, as well as senators such as Balbus. The password was ‘liberty’ and the day of the murder was chosen: 24 January, the last day of the Palatine Games.

The conspirators chose their place well. A makeshift amphitheatre had been erected in the Emperor’s palace, served by narrow galleries and passageways. The conspirators took oaths to either kill Caligula there or, if they failed, kill themselves. I became their shadow. The only person Agrippina had told me to take care of was Progeones, I had only glimpsed that awful little creature from afar. Progeones was now hated by everyone. He was regarded as Caligula’s dagger man and constantly carried a list of those the Emperor wished to condemn.

On the morning of the twenty-fourth, Cassius arranged that I join the Emperor in the imperial box at the games. Caligula was in good form, shouting, gesticulating, throwing coins at the mob. He espied me, called me over and clapped me on the shoulder.

‘I’ve had enough of your miserable face, Parmenon. It’s back to Pontia for you. Tell my bitch of a sister that I have been thinking about her more often than I should.’

I kissed the Emperor’s hand and withdrew. I glanced quickly at Progeones. He seemed nervous and ill at ease, and I wondered if he had a spy amongst the conspirators. Caligula then went to a makeshift altar and sacrificed a flamingo for good luck. When some of the blood splashed on his toga, he wiped it off and licked his fingers. He resumed his seat, now and again calling over a senator to kiss his slippered foot.

I glanced around. Chaerea, in full dress armour, tense as a bow string, stood next to the door clutching his sword. The strike had been planned for the end of the day, but the tension was already palpable. I left my seat and crossed to Chaerea.

‘It must be done now,’ I urged. ‘Progeones suspects something.’

Chaerea shook his head, his pallid face soaked in sweat. I glanced down the tier of seats. Castor and Pollux and other members of the German bodyguard now ringed the Emperor. The morning drew on. The fighters in the amphitheatre were lacklustre. Caligula, bored, climbed over the balustrade and into the arena, accompanied by Castor and Pollux. The Emperor grabbed a sword and showed one gladiator how to fight. His opponent, overcome with fear, fell to his knees and begged for mercy. The Emperor neighed with laughter and drove his sword deep into the man’s throat. Helped by his bodyguards, Caligula climbed back into the imperial box.

‘I am hungry!’ he shouted. ‘I want something to eat!’

He turned round and his eyes met mine, a cool, sane look. I’ve always wondered if Caligula knew he was going to die that day.

‘Parmenon!’ he shouted. ‘Join me. I have fresh messages for my sister.’

He shoved his guards aside and climbed the steps towards me. Castor and Pollux followed. For a while confusion reigned, as senators leapt up and wondered whether they should accompany the Emperor or not. Caligula took me by the arm and pushed me out. Chaerea and the others clustered by the doorway. There were a number of underground entrances, some for the crowd, others for the Emperor and his important guests. Caligula went towards one of the latter, and I seized my opportunity.

‘No, your Excellency, it is safer down here.’

Caligula didn’t object. He turned quickly and we went down a narrow passageway towards a pool of light. Footsteps echoed behind us. The Emperor thought it was his bodyguard: in fact it was Chaerea and the rest.

I heard shouts in German. The Emperor, alarmed, peered back through the gloom.

‘What is this?’ he exclaimed.

Chaerea’s sword was already drawn. I pushed the Emperor away from me. Caligula staggered back, his eyes rounded with terror. He lifted his hand to fend off the blow but Chaerea was too swift, and he sliced the Emperor between neck and shoulder. As the Emperor collapsed to his knees, a second blow slashed his jaw. Caligula gave a cry and collapsed on one side. The rest joined in, a melee of screams and shouts, daggers and swords rising and falling. The alarm had been raised, and the German bodyguard, led by Thracian officers, thronged down the passageway, shields up, swords out. In the confusion they had first chosen the wrong way. I glanced down. Caligula was dead, his corpse saturated in blood. Some of the conspirators chose to defend themselves as the Germans closed in. I decided to flee and was soon out in the sunlight, running back towards the city.