Agrippina led the meeting, as Macro’s men guarded the door.

‘Well,’ she demanded of Charicles. ‘Is he dying?’

‘I don’t believe so, Domina, it’s just a fit.’ Charicles tapped his forehead. ‘More of the mind than the body.’

‘Has he been poisoned?’ Progeones lisped.

Charicles stared at Agrippina. The valerian was a secret: I begged Agrippina with my eyes not to mention it.

‘He’s not been poisoned,’ Charicles confirmed, ‘but he’s in a deep sleep. He may die or. .’ He shrugged.

‘What can we do?’ Agrippina asked.

‘If he dies,’ Macro broke in, ‘Gemellus still lies under house arrest, a possible heir to the throne.’

Agrippina clutched her belly. During those few tense moments I discovered the full extent of Agrippina’s secret ambition: she would have a son, who would ascend to the purple, and when he was Emperor, she would be the one to control him. Anyone else — whoever they were — would simply wear the purple until she and her son were ready.

‘No!’ She shook her head. ‘Macro, send messages to the legion commanders!’

‘Oh, they’ll be loyal enough,’ Macro laughed. ‘And the Praetorian Guard take their orders from me.’

Agrippina sat, sucking on her lips.

‘Let it be. Let it be,’ she murmured.

Agrippina stayed on in the palace where she and Macro managed everything. The news of Caligula’s illness spread through Rome, and people grew hysterical, or pretended to, with grief. The Palatine was besieged by mobs eager for news. Five days after that infamous banquet, Caligula awoke. He pulled himself up in bed and stared around, smacking his lips. His eyes were clear with a mischievous, malicious look, as if it had all been a game. As Agrippina carefully explained his illness. Caligula heard her out, nodding wisely, before demanding to be washed and fed and have Drusilla sent to him.

Caligula kept glancing at Agrippina out of the corner of his eyes, and now and again he would wink at me as if we were sharing a joke. I’ll be honest, the look on that man’s face made me shiver. Whatever soul Caligula possessed before, had died during those five absent days, and thereafter the king of demons controlled his mind.

‘So, he said he’d sacrifice himself, did he?’ he declared, tapping his chin and referring to a Roman citizen Afraneus. ‘Promised to commit suicide if I recovered? Well I have, haven’t I, Parmenon?’ He grinned and winked, clapping his hands. ‘The Gods have blessed me. So, Afraneus must fulfil the vow!’

It was the beginning of the terror.

The following day Afraneus was arrested. Naked, except for a loin cloth, he was paraded through Rome and tossed off the Tarpeian rock. Another official had reputedly offered to fight as a gladiator if Caligula recovered. The Emperor kept him to his promise and made the unfortunate man battle it out in the amphitheatre. Drusilla and Agrippina were in no danger, but the atmosphere at court became tense and watchful. Caligula showed little overt hostility to anyone in particular until one night, at a banquet, he abruptly turned on Macro who had been offering advice on some petty matter.

‘How dare you lecture me?’ Caligula roared. ‘How dare you set yourself up as my superior?’

‘That is not true,’ Agrippina intervened.

‘Isn’t it?’ Caligula yelled.

The Praetorian Prefect leapt to his feet and made ready to leave.

‘You won’t get far!’ Caligula shouted.

Two German auxiliaries, favourites of the Emperor, appeared in the doorway. Tall and blond-haired, they looked like twins and were nicknamed Castor and Pollux. Macro spun round, and glanced beseechingly at Agrippina. She could only stare sorrowfully back. We’d been invited to these banquets for days following the Emperor’s recovery and until now nothing had happened. Caligula had lulled our suspicions until springing like a hunting panther.

‘We should kill him now,’ Agrippina whispered to me.

She moved further up the couch to elicit support from Drusilla but that empty-head was drunk and half asleep, her face pressed against the headrest.

Macro tried reasoning with Caligula. ‘I have only ever wanted to help. .’

‘Assassin!’ Caligula screamed. ‘You are under arrest! The charge is treason!’

The mercenaries seized Macro and dragged him from the room. I never saw him again: he was dead by the following morning. Macro’s fall was the sign for a new bloodbath. Silenus, Caligula’s former father-in-law, was arrested and openly accused in the Senate: his response was to cut his throat in front of all his colleagues. Gemellus, Tiberius’s grandson, was released from house arrest, but then his fate followed the same pattern as Macro’s. He was invited to a banquet, where Caligula shared his couch, and sniffed the young man’s breath.

‘What are you doing?’ Caligula screamed. ‘Taking antidotes for poison? Are you accusing me of trying to poison you? You, who prayed for my death!’

‘I have not prayed for your death,’ Gemellus replied. ‘I take no antidote, it’s cough medicine!’

Caligula refused to accept this. ‘It’s an antidote!’ he insisted.

Gemellus, give him his due, realised his time had come. ‘There is no antidote against Caesar,’ he bravely retorted.

He was allowed to leave the banquet, but the following day Praetorians were sent to his house and forced him to open his veins.

Caligula’s conduct became wilder and more outrageous. He attended the marriage of a noblewoman Orestilla, where he sat next to the bride and sent a note to the bridegroom, inscribed ‘Don’t make love to my wife!’

He ordered Orestilla to be taken to his own quarters and married her himself. A few months later he divorced the woman but ordered her never to make love to any man for as long as the Emperor lived. Sometimes his conduct was simply malicious. He made his uncle, Claudius, the constant butt of his jokes. Caligula would throw olive, fig and date stones at him and put slippers on his hands as he dozed in a wine-drenched sleep. Caligula would roar with laughter when the old man woke and tried to rub his face with his hands.

Agrippina ignored all this. She withdrew from court, more concerned that nothing would occur to upset the impending birth of her child. The boy was born in December, after a difficult delivery. The portents were good, though Agrippina kept them quiet. ‘Now is not the time,’ she whispered to me, ‘to remind my mad brother that there’s another Caesar in Rome.’

‘What shall we do?’ I urged.

‘We must wait,’ she replied. ‘The same as we had to do with Tiberius on Capri. .’

At first I admired my mistress’s cunning and coolness, until two events abruptly changed this. In June the following year Drusilla suddenly died, and Caligula’s grief was ostentatious, bloody and dangerous. She was granted a public funeral, and during the time of official mourning, it became a capital offence to laugh, bathe, or even dine with one’s family. Caligula tried to console himself for the loss of his sister. He married a disreputable noblewoman, Lollia Paulina, who insisted on turning up at dinner parties drenched in jewels and pearls worth millions of sesterces. She actually made her slave carry the receipts around to show would-be admirers how much she was worth. Caligula soon tired of her and dear Lollia went the way of all the rest. Next he married Caesonia, a woman of high birth and low morals, who already had a number of children by other husbands. When I informed Agrippina of this, her rage was as surprising as it was fierce. She leapt off the couch, dropping all the accustomed poise of a noblewoman in retirement. She paced up and down her bedchamber, beating her fists against her thighs.

‘He is mad but he can still beget!’ she exclaimed. ‘And never forget that Caligula is the son of Germanicus. Or might be,’ she added in a half-whisper.

‘I beg your pardon, Domina? What did you say?’

Agrippina looked over her shoulder at me, with that lopsided smile on her face. She went over and kicked the door shut.