I am not a complete idiot. This broad-bellied cockleshell looked as if it had been lying here a long time. I did carry out a thorough inspection for stakes stuck through its planking, or bungholes with missing plugs. There was nothing wrong with my convenient coracle-or at least, nothing a highly cautious landlubber could see.

I found a spare oar leaning against someone's worm-eaten mooring post, then another paddle under the skiff when I managed to lever it right side up. I shouldered it down to the water's edge, helped by the shop boys' girlfriends, who were happy to fill time respectably before it grew dark and their lads started getting ideas. I tossed a last look back for Larius or Petro but there was no sign, so I climbed in, swayed on the prow with an effort at bravado, and let the girls shove me off.

It was a clumsy piece of carpentry. The clod who built it must have been feeling off colour that day. It bobbed in the wavelets like an intoxicated fruit-fly dancing at a rotten peach. It took some time to get the hang of keeping this mad thing pointing forwards, but in the end I began to make some progress from the shore. The breeze in my face was slight, though not helping much. My purloined oar had a bitten blade, and the other paddle was too short. The glare off the sea added a new glaze to my sunburn while it also made me squint. I didn't care. The reluctance Aufidius Crispus had demonstrated to facing an innocent interview fired my determination to get on board the Isis and find out what the big mystery was supposed to be.

I dug deep and pushed out steadily until I had halved the distance from Oplontis to the ship. I congratulated myself on my spirit and initiative. Vespasian would be proud of me. I came near enough to read her name, painted high on the prow in angular Greek lettering… At about the same time as I grinned triumphantly, a completely different sensation impinged on me.

My feet were wet.

Almost as soon as I noticed the cold, I was standing in seawater up to the ankles and my luckless skiff was foundering. Once the Tyrrhenian Sea discovered it could seep through the dried planks, it rushed in on all sides and my vessel sank beneath me rapidly.

There was nothing I could do but shut my eyes, hold my nose, and hope some sea nymph with a nice nature would pull me out.

Larius pulled me out. Wallowing with a Nereid would have been more fun.

My nephew must have seen me set off and been on his way after me before I sank. Remember his father was a boatman; Larius had been dandled in the Tiber even before he was weaned. He could swim when he was two. He never used the sinister, silent, Batavian crawl which the Army teaches. My nephew had a horrible style, though a thrashing turn of speed.

When I came round, with the feeling of having been violently engulfed then flailed against a concrete wall, I could tell how Larius had achieved my rescue by the agonies I had acquired as a result. I had a bruised throat where he had heroically gripped me, and a gashed ear where he had crashed my head against a mooring stage. The backs of my legs were raw from being dragged over the pumice up the beach, and I was being pumped back to life by Petronius Longus, applying his full bodyweight. Afterwards, I felt perfectly happy to lie still for a long time, considering my sore windpipe and pummelled flesh.

'Think he'll live?' I heard Larius ask; he sounded more curious than concerned.

'Reckon so.'

I let out a grunt to inform Petronius that he could now feel free to amuse himself with jokes at my expense. His unmistakable fist thumped my shoulder.

'He's been in the Army. Why can't he swim?' That was Larius.

'Oh… the week we did watersports in basic training, Marcus was confined to barracks on fatigues.'

'What had he done?'

'Nothing serious. We had a high-handed junior tribune who got the idea Marcus had been playing around with his girl.'

There was a pause. 'Had he?' Larius eventually enquired.

'Oh no! In those days he was much too shy!' Untrue. But Petronius does not believe in corrupting the young.

I rolled over away from them. I peered seawards for the Isis through swollen eyes, but she had gone.

The low evening sun savaged my legs and shoulders, as it came glancing through my lightly bloodstained marinade of brine. I lay face down on the beach thinking about death by drowning and other cheerful things.

Far away at the water's edge I could hear Petro's three young daughters shrieking with delight as they chased each other fearlessly in and out of the dreadful sea.

'Anyway!' Petronius chaffed Larius. 'How come you're always extricating this fool when disaster strikes?'

Larius blew his nose. He took his time answering but when he did I could tell he was enjoying it.

'I promised his mother I'd look after him,' he said.

Next day my friends decided I must be taught to swim.

It was probably a bad idea for them to try giving lessons to someone who still went rigid at any possibility of going under with seawater filling his lungs. Still, they all took it seriously so I attempted to co-operate.

It was hopeless. Petronius could hardly hold me up by the back of my tunic as he did with his children, and when Larius tried making water wings from inflated wineskins he just wore himself out blowing them up.

Nobody laughed, however. And nobody condemned me when I climbed back out of the water, walked up the beach, and sat down alone.

I stayed by myself, morosely flipping pebbles at a hermit crab. I skimmed them to miss, since I was not in the mood for outright cruelty; the crab found a shell of his own and started to build an extension to his house.

We were eating when Helena came.

We had left Ollia with the children, apart from Tadia who had been badly stung by a jellyfish so we brought her with us, still flushed and miserable (the poor mite had sat on it). Larius stayed with Ollia; I overheard the two of them discussing lyric poetry.

We ate at an open-air winery where they also served seafood. Petronius had inspected the kitchen at Silvia's behest; I won't pretend the proprietors welcomed him, but he had the knack of getting into places wiser men would have left alone, then being treated for ever as a friend of the management.

Helena had seen us and was out of her sedan chair by the time I came up. I heard her instruct the servants to amuse themselves with a flagon and come back for her later. They stared at me, but I had little Tadia half-asleep in my arms so I looked harmless.

'Personal delivery, ladyship?'

'Yes-I'm having a mad burst of energy-' Helena Justina sounded breathless, but that may have been the effort of extracting herself and my mother's new bucket from the sedan chair. 'If I were at home I'd be tackling those jobs everyone avoids, like spring-cleaning the pantry where we keep the fish-pickle jars. In someone else's house it seems impolite to suggest their kitchen amphorae may leak…' She was dressed plainly in grey though her eyes were very bright. 'So I may as well deal with you-'

'Oh thanks! Like a nasty sticky ring on a floor slab, waiting to be scrubbed away?' She smiled. I muttered grittily, 'When you smile you have beautiful eyes!'

She stopped smiling. But she still had beautiful eyes.

I looked away. Out to sea. Round the Bay. Up at Vesuvius-anywhere. I had to look back. Those eyes of hers finally met mine directly.

'Hello, Marcus,' she said carefully, like someone humouring a clown.