I turned to Paccius. `You will have gathered from our approach to the judge yesterday that we have had to reconsider the evidence.'

`You accept that Calpurnia Cara is innocent?'

`No, I think she has a lot to answer for. But we shall withdraw our murder charge.'

`My client will be delighted,' Paccius said mildly. He had no need to gloat and he was too subtle to mention huge damages. His calm air of self-assurance made the prospect all the more frightening.

I pressed on with trying to negotiate. `Silius, our new evidence means your petition against Negrinus will not hold up. He did not kill his father. If you go for it, we can wipe you out. Be grateful: we are preventing you from embarking on a fruitless case.' Silius laughed. Paccius pretended to be politely absorbed in something else, while Honorius looked embarrassed. `But you still need to prove formally that Rubirius Metellus did not commit suicide, so you can claim your compensation. We know what happened. I can offer you a bargain -'

`I'm not buying,' said Silius, enjoying himself. `I know that Metellus was murdered by Saffia.'

Honorius was staring at the ground. Since I arrived, an almond cake crimped with one forlorn bite had lain untouched in front of him. I was right: Silius had bought him. Now I knew how. Paccius, in league with Silius despite their alleged feud, had promised Honorius he would waive any Calpurnia compensation which Marponius awarded against him. So Honorius had given this pair my saleable information.

I kept my thoughts to myself. Expressionless, I stood up and said I would see them in court.

Maybe Honorius had a conscience – though if so, it would not last among those liver-pecking eagles. As I went back across the Forum to the Basilica, he did rush after me. He was agitated.

`Falco! Just let me say this: my leaving is not as bad as you think.'

`Oh no?' At the base of a statue plinth I rounded on him. `You mean, you have not dumped us because we're in trouble – and you did not tell those bastards we identified Saffia as the killer?'

`I've left you,' he conceded. `And the timing stinks. But they already knew about Saffia.'

I paused. `They knew?'

`Paccius knew Bratta bought the hemlock for her. And she told Bratta she wanted it for her father-in-law.'

`Well, that was correct!' I stopped. `How did Paccius know?'

`When Saffia left Negrinus, Paccius advised on their divorce. He sent Bratta to help with her removals. She knew what kind of work Bratta did. When she asked about buying poison, Bratta reported straight back to Paccius.'

`So did Paccius encourage – or better still, order – Bratta to help acquire the hemlock…?' Honorius and I knew we would find no answer to that red hot question.

Paccius Africanus was tangled up in this business to a degree that I would call unethical – had ethics had any place in his world. If he was party to Bratta's purchase, we could charge him with incitement, or with being an accessory to murder. But I would never prove it.

I was wondering whether Paccius realised Bratta might have killed Spindex. I doubted if Honorius knew. Even Paccius might be in the dark: Bratta may have acted on his own initiative. None of them knew yet that Bratta was wanted by the vigiles. Perhaps a sordid backstreet killing which Paccius had never authorised might yet be used to topple the informers' elaborate schemes. `Bratta has disappeared, Honorius. Do they know where he is?'

`Bratta? Paccius has the rogue as a house guest at his own mansion.' Hmm. I wondered if we could lift Bratta. Not that Petronius Longus, whose remit was the Aventine, would agree to go north of the Forum. He wouldn't want to raid an ex-consul's grand abode either. I would have to extract Bratta myself.

`One last thing – Did they both know about Saffia? Paccius and Silius?' Ashamed of his new compatriots, Honorius nodded. `And did they know from the start?'

`I suppose they may have done.'

At long last I saw it all. If the two informers knew all along who killed Metellus, everything since had been a set-up. They had deliberately failed to prosecute Saffia herself They had toyed with Rubiria Juliana, then worked around to Metellus Negrinus. They manipulated me, hoping I would make a counter-charge – one they always knew could not hold up. They could have stopped the Calpurnia prosecution at any time. They had Bratta as a star witness. With his tale of buying the poison for Saffia, they were all set to run up their compensation claim against Falco and Associates.

As it turned out, being ethical idiots, Falco and Associates had saved them the bother.

I wondered if Paccius and Silius had deliberately planted Honorius amongst us as a spy. For a moment I even wondered if they had primed the steward to spout his story about Saffia's quails now, at a time that suited them. However, I guessed their information all came from Bratta.

Something else struck me. Maybe the two informers' crafty tricks went back much further than I had realised. If they knew about Saffia and the quails, maybe they knew whatever secret Saffia had used to blackmail the Metelli.

Finally, I began to grasp the scale – and the long timescale – of their devious plans. They had lined up the Metelli as victims years ago.

I, too, could take advantage of my opponents' weaknesses. When pushed, I abandoned all scruples. At the Basilica Julia, I left a message for Petronius. I dared not say much; any court official might be in Paccius' pay. But I asked Petro to wait for me outside. That sounded innocuous. Then I set off alone.

At the elegant home of Paccius Africanus, I gave a false name. The suave slaves were not competent enough to remember me. They accepted my fake byline, though they then denied that Bratta was indoors. I sent in word for him anyway. I said Paccius had run into setbacks and wanted Bratta urgently at the court.

Bratta came out eventually. Emerging from a doorway, I followed him. He walked with an informer's gait, confident but unobtrusive. He was checking for observers, but he never spotted me. I grew so jumpy I found myself glancing behind me in case Bratta had brought a shadow, who might now be tailing me… Apparently not. He just walked on, sometimes swapping the side of the street, but not bothering to use double-backs. He was methodical, but must have felt secure.

When he reached the Forum, he seemed to grow more wary. He crossed the historic piazza by way of the narrow, little-used path between the Regia and the back end of the Temple of Divine Julius. From the shadow of the Arch of Augustus, he checked for trouble, hoping he would see it first. He failed to spot a tall, quiet man in brown standing immediately above him on the steps of the Temple of Castor: Petronius Longus. Petro had seen Bratta lurking by the Arch, and he had seen me.

Bratta stepped out on to the Sacred Way. Lifting him would be easy. What would be hard was lifting him without the public noticing.

I moved closer. Petronius remained still. All around us were people at their normal tasks, weaving to and fro across the Forum in intricate patterns. Bratta was too hesitant; a garland-seller bumped into him. He had lost his rhythm; he was knocking against people. He had sensed his mistake. He was nervous. This was too public, and he was starting to doubt that my message had been genuine. But he still had not seen us. I signalled to Petro and we both moved in.

We reached him together. We had surprised him, but he was extremely strong. We took him, after a struggle. He was almost at the Basilica steps by then. He had kicked me in the guts, and he had bitten Petro. There was blood streaming down his tunic, where he had ignored my threatening knife. Petronius had finally subdued him, using vigiles aggression.

Bratta had never called for help. A loner by trade, he may not even have thought of it. As we hustled him away down a sidestreet, nobody saw us go.