'For the money then?' Larius sounded puzzled.

'Money is freedom, lad.'

If he had not been too soft to take the knocks and too shy to handle the women, this Larius would have made a good informer; he could persist with a line of enquiry until the person he was questioning wanted to thump his ear. (Also, his outsize puppy feet were bearing up to the Oplontis road far better than mine; I had a badly sore toe.)

'What do you want money for?' he grilled me relentlessly.

'Fresh meat, tunics that fit properly, all the books I can lay my hands on, a new bed with all four legs the same length, a lifetime's supply of Falernian to guzzle with Petro-'

'A woman?' he interrupted my happy flow.

'Oh, I doubt it! We were talking about freedom, weren't we?'

A vaguely reproachful silence ensued. Then Larius murmured, 'Uncle Marcus, don't you believe in love?'

'Not any more.'

'There is a rumour you were smitten recently.'

'The lady in question left me. Due to my shortage of cash.'

'Oh,' he said.

'Oh indeed!'

'What was she like?' He was not even leering; he sounded genuinely intrigued.

'Marvellous. Don't make me remember. Right now,' I suggested, feeling older than my thirty years, 'what I'd settle for is a big copper bowl full of piping hot water to soak my tender feet!'

We trudged on.

'Was the lady-' persisted Larius.

'Larius, I'd like to pretend I'd drag off my boots for her, and walk barefoot over a cinder path for another hundred miles. Frankly I stop feeling romantic when I get a bulging blister on my toe!'

'Was she important?' Larius finished stubbornly.

'Not very,' I said. (On principle.)

'So not,' persisted Larius, '"she whom, through living, gives your life its sweet reason"…? Catullus,' he added, as though he thought I might not know. (I knew all right; I had been fourteen myself once, and stuffed to the gills with dreams of sexual conquest and depressing poetry.)

'No,' I said. 'But she could have been-and for your private information, that's a Falco original!'

Larius murmured quietly that he was sorry about my sore toe.

As we approached the inn at Oplontis, I saw two skulking figures on the dark beach outside.

I said nothing to Larius, but led him round in the shadows to slip in through the stable block. We found Petro bedding down the ox. Poor Nero was almost asleep on his cloven feet; after hauling my lead he was too tired even to bend his neck to the feeding trough so Petronius Longus, the hard man of the Aventine watch, was enticing wisps of hay into the beast's huge mouth with murmurs of loving encouragement.

'Just a bit more, precious…' we heard him coax, in his tone for spooning broth down a sad child. Larius giggled; Petro was unabashed. 'I want to take him home in good condition!'

I explained to my nephew that Petronius and his brother (who was a tireless entrepreneur) had formed a syndicate to buy this ox with three of their relatives; it always caused bad feeling when Petro popped up at his country cousins' farm to borrow his investment.

'How is Nero meant to be shared then?' Larius asked.

'Oh, the other four tell me it's a leg each for them, and I get his balls,' Petronius replied gravely; the big-city innocent. He shoved in a last sheaf of hay then gave up.

Larius, who was sharp but not yet sharp enough, squatted down to check, then leapt up proclaiming, 'He's an ox! He's been castrated; he hasn't any-'

Catching sight of our faces, he clammed up as the joke slowly dawned.

'Anyway,' I commented, 'this ox must be four years old; what lunatic named him Nero while the Emperor was alive?'

'I did it,' Petronius answered, 'when I picked him up last week; the others call him Spot. Apart from the fact he has a curly topknot and heavy jowls, whoever clipped his equipment bungled it, so he shares with our glorious late Emperor indiscriminate lechery: bullocks, heifers, five-barred gates; the fool will jump on anything-'

Petronius Longus had fierce views on government; trying to keep public order among citizens who knew they were ruled by a mad lyre player had filled him with frustration, though this was the only open political gesture I had seen him make.

Trailing a long dribble of saliva, Nero, who hardly looked equal to jumping on anything, closed his dun-coloured eyelids and leaned against the stall; changing his mind, he lunged forward fondly towards Petronius. Petro jumped back, and we all jammed up the gate, trying to look nonchalant.

'One bit of news,' I told Petro. 'Our ship is called the Isis Africana-Larius has been using his initiative.'

'Intelligent boy!' Petro applauded, pinching his cheek (knowing Larius hated it). 'And I've got something for you, Falco. I stopped by a turning to one of those upland villages-'

'What had you stopped for?' Larius interrupted.

'Don't be nosy. Picking flowers. Falco, I was asking one of the locals about who is important hereabouts. Do you recollect that antiquated ex-consul we investigated in connection with the Pertinax conspiracy?'

'Caprenius Marcellus? His father? The invalid?'

I myself had never met him but I certainly remembered Marcellus: one of Rome's elderly senators, with seven previous consuls in his glorious pedigree. He had possessed an enormous fortune and no heir, until Pertinax caught his eye and was taken on as his adopted son. (Either he was very shortsighted, or being descended from consuls did not make a senator astute.)

'I saw the old bird at Setia,' Petro reminisced. 'Good wine country! But he was rich as Crassus. He owns vineyards all over Campania-one up on Vesuvius.'

'Officially,' I mused, 'Marcellus was cleared of conspiracy.' Even though he owned the warehouse the plotters used for storing their bullion, having a good pedigree and a massive fortune had largely protected him; we had made routine enquiries, then respectfully backed off. 'He's supposed to be much too ill for politics-and if so he won't be here; he couldn't travel if the story's genuine. His place might be worth a visit though-'

It struck me that this villa rustica could be harbouring Barnabas. In fact, a villa on Mount Vesuvius whose owner was ill elsewhere could provide a perfect hideaway. I was sure Petronius reckoned the same, though in his cautious way he said nothing.

Changing the subject, I mentioned the two secretive figures I had noticed earlier on the beach. Planting Larius behind us, Petro and I armed ourselves with a lantern and marched out to look.

They were still there. If they were lying in wait, they were completely unprofessional; a murmur of surreptitious voices met our ears. As our footfalls disturbed them, the smaller shadow detached itself and ran into the inn with a squeak. My nose twitched at rancid, second-rate rosewater, then I glimpsed a familiar top-heavy bosom and anxious, moon-shaped face. I chuckled.

'Ollia's quick off the mark! She's found her fisherboy!'

She had too. He sauntered up past us with the self-assured, curious stare these gigolos always possess. A dim girl's dream. He had the lovingly tended haircut, short sturdy legs and brawny brown shoulders that were made for showing off to city girls as he practised hurling nets.

'Goodnight!' Petro called firmly, in the voice of a watch captain who can handle himself. The young lobster-catcher sloped off without answering. His features were not up to much by Aventine standards, and I guessed that as a boatman's apprentice he was pretty slovenly.

We left Petronius in the courtyard: a man who took life seriously, strolling round to see that all was in order before he turned in.