Helena and Jason watched keenly as Thalia strode up the ramp to comfort the elephant. We could hear her berating its trainers; she loved animals, but evidently believed in producing high-class acts by a regime of fear- in her staff, that is. Like me, they had now decided the exercise was doomed. Even if they could entice their ungainly grey acrobat out over the void, the rope was bound to snap. I wondered whether to point this out. No one would thank me, so I stayed mum. Scientific information has a low rating in Rome.

Helena and Jason were getting on well. She had had some practice with untrustworthy reptiles, after all; she knew me.

Since nothing else was required, I started to think. Informers spend a lot of time crouching in dark porticos, waiting to overhear scandals that may bring in a greasy denarius from some unlikeable patron. It's boring work. You are bound to fall into one bad habit or another. Other informers amuse themselves with casual vice. I had grown out of that. My failing was to indulge in private thought.

The elephant had now been fed a sesame bun, but still looked dismal. So did I. What was on my mind was the job had just been offered. I was thinking up excuses to turn it down.

Sometimes I worked for Vespasian. A new emperor, sprung from a middle-class background and wanting to keep a canny eye on the nasty snobs of the old elite, may need the occasional favour. I mean, a favour of the kind he won't be boasting about when his glorious achievements are recorded in bronze lettering on marble monuments. Rome was full of plotters who would have liked to poke Vespasian off the throne, so long as they could make the attempt with a fairly long stick in case he turned round and bit them. There were others annoyances, too, that he wanted to be rid of- dreary men fastened into high public positions on the strength of mouldy old pedigrees, men who had neither brains nor energy nor morals, and whom the new Emperor intended to replace with brighter talent. Somebody had to weed out the plotters and discredit the idiots. I was quick and discreet, and Vespasian could trust me to tidy up loose ends. There were never repercussions from my jobs.

We first took each other on eighteen months ago. Now, whenever I had more creditors than usual, or when I forgot how much I loathed the work, I agreed to imperial employment. Though I despised myself for becoming a tool of the state, I had earned some cash. Cash was always welcome in my vicinity.

As a result of my efforts Rome and some of the provinces were more secure. But last week the imperial family had broken an important promise. Instead of promoting me socially, so I could marry Helena Justina and appease her disgruntled family, when I had called to claim my recompense from the Caesars they kicked me down the Palatine steps empty-handed. At that, Helena declared that Vespasian had given me his last commission. He himself failed to notice that I might feel slighted by so small a thing as mere lack of reward; within three days here he was, offering me another of his diplomatic trips abroad. Helena would be furious.

Luckily, when the new summons to the Palace came, I was heading downstairs from our apartment on my way to pick up gossip at the barber's. The message had been brought to me by a puny slave with coarse eyebrows joined together above hardly any brain – up to standard for Palace messengers. I managed to grab the back of his short tunic and march him down to the ground-floor laundry without Helena seeing him. I paid a small bribe to Lenia, the laundress, to keep her quiet. Then I hurried the slave back to the Palatine and gave him a stern warning against causing me domestic inconvenience.

'Stuff you, Falco! I'll go where I'm sent.'

'Who sent you then?'

He looked nervous – with reason. 'Anacrites.'

I growled. This was worse news than being asked to attend Vespasian or one of his sons.

Anacrites was the official Chief Spy at the Palace. We were old antagonists. Our rivalry was the most bitter kind: purely professional. He liked to see himself as an expert at dealing with tricky characters in dangerous locations, but the truth was he led too soft a life and had lost the knack; besides, Vespasian kept him short of resources, so he was beset by pathetic subordinates and never had a ready bribe to hand, Lack of small change is fatal in our job.

Whenever Anacrites bungled some sensitive commission, he knew Vespasian would send me in to put his mistakes right. (I provided my own resources; I came cheap.) My successes had aroused his permanent jealousy. Now, although his habit was always to appear friendly in public, I knew that one day Anacrites meant to fix me for good.

I gave his messenger another piece of colourful career advice, then stomped in for what was bound to be a tense confrontation. Anacrites' office was about the size of my mother's lamp store. Spies were not accorded respect under Vespasian; he had never cared who might be overheard insulting him. Vespasian had Rome to rebuild, and took the rash view that his public achievements would sufficiently enhance his reputation without the need to resort to terror tactics.

Under this relaxed regime Anacrites was visibly struggling. He had equipped himself with a folding bronze chair, but sat crushed up in one corner of the room in order to make space for his clerk. The clerk was a big, misshapen lump of Thracian sheep's fat in a flashy red tunic that he must have stolen off a balcony parapet whilst it was hanging out to air. His huge feet took up most of the floor in their ungainly sandals, ink and lamp oil spilled on their thongs. Even with Anacrites sitting there, this clerk managed to suggest that he was the important person visitors ought to address.

The room gave off a faintly unprofessional impression. It had an odd scent of turpentine corn plasters and cold toasted bread. Scattered all around were crumpled scrolls and wax tablets that I took to be expenses claims. Probably claims by Anacrites and his runners which the Emperor had refused to pay. Vespasian was notoriously tight, and spies have no sense of discretion when requesting travel refunds.

As I went in, the master of espionage was chewing a stylus and staring dreamily at a fly on the wall. Once he saw me, Anacrites straightened up and looked important. He hit his knee with a crack that made the clerk wince, and me too; then he sank back pretending to be unconcerned. I winked at the clerk. He knew what a bastard he worked for, yet openly dared to grin back at me.

Anacrites affected tunics in discreet shades of stone and buff as if he were pretending to merge into backgrounds, but his clothes always had a slightly racy cut, and his hair lay oiled back from his temples so precisely I felt my nostrils curl. The vanity in his appearance matched his view of himself professionally. He was a good public speaker, able to mislead with easy grace. I never trust men who have nicely manicured fingernails and a deceitful way with words.

My dusty boot knocked into a group of scrolls. 'What's this? More poisonous accusations against innocent citizens?'

'Falco, just you attend to your business, and I'll look after mine.' He managed to imply that his business was deeply relevant and intriguing, while my motives and methods smelt like a barrel of dead squid.

'A pleasure,' I agreed. 'Must have received the wrong message. Someone claimed you needed me – '

'I sent for you.' He had to act as if he were giving me orders. I ignored the insult – temporarily.

I pressed a small copper into his clerk's hand. 'Go out and buy yourself an apple.' Anacrites looked furious at me interfering with his staff. While he was still thinking up a countermand, the Thracian skipped. I slumped on to the clerk's vacant stool, spreading myself across most of the office, and grabbed a scroll to look through nosily.