We clambered uphill on a short roadway to a large walled enclosure. Albia skipped on ahead, though Claudia was breathing hard so Helena and I slowed our pace for her. Inside the walls, the sanctuary was planted with gardens. Even in December this was a pleasant place to stroll among the topiary, quiet arbours and statues, and the fine lake view beyond. Around the fane were other facilities, including an empty theatre.

'y ou look too virile,' Helena told me. 'We can't take you. They will know I spend a lot of time fending you off and trying not to conceive.' I raised an eyebrow silently reminding her that there had been no fending off last night. Helena blushed. 'Jacinthus will be acceptable as our bodyguard.' Jacinthus was tiresomely excited; he was hoping that a wild boar would thrust its snout from the undergrowth – not so he could turn it into escallops and terrine as he should do, but so he could fight it. 'He can find you when we're finished. Go and amuse yourself somewhere, Marcus, and we'll meet later.' 'How long will you be?' 'Not long.' 'Any husband knows what that means.' We could see that there were pilgrims in the sanctuary. I reckoned there would be a slow queue at the fertility shrine. The priests would keep everyone waiting, to unsettle them and make them suggestible – or as they would say, to allow the shrine's calming influence to soothe them.

'Oh don't make a fuss. Go and play in the woods, Falco – and take care!' Woods did not frighten me.

I walked about for several hours. I searched all the small shrines, temples and recreational facilities, a task which was as tedious as I expected, then I strolled down weedy paths among the trees. Scowling with cold and boredom, I listened to the rustles and sighs that nature devises to unnerve town-dwellers who find themselves out in the open. I remembered this from Germany. We had spent weeks trailing through miles of forest, growing more and more leery; I knew how it felt to be quite alone in the woods, even for a short time. Every crack of a twig makes your heart bump. I hate that smell of old animal trails and suspicious fungi. I dread that sense, every time you enter a clearing, that somebody or something rank has disappeared on one of those damp paths moments before you – and is still close by, watching with hostile eyes.

I could understand how dark legends about Nemi had sprung up in Rome's prehistory. This spot had been sacred for centuries. In times gone by, there was always supposed to be King of the Grove, a chief priest, who came here first as a runaway slave; he plucked a golden bough from a special tree, which would only yield to the true applicant. He would find and kill in single combat the previous King of the Grove. Then he could only wait anxiously for the next runaway to arrive through the spectral mists and kill him… Those bloodthirsty days had supposedly been ended when the Emperor Caligula casually decided that the current incumbent had been in post too long, so he sent a tougher man to depose him and make rex Nemorensis a civic position, presumably with the normal terms and conditions.

Public service has its dark side. The pay is always meagre and the pension rights are rubbish. Do your job well, and some mediocrity always gets jealous, then you end up being shifted sideways, to make way for a half-baked management favourite who cannot remember the old days and who has no respect for the gods…

Caligula liked Nemi. He used the place as a decadent retreat. He had two stupendous barges built to float on the lake, floating pleasure palaces. I had heard that those barges were larger and even more extravagantly decorated than the gilded state barges used by the Ptolemys on the River Nile; their fabulous on-board accommodation included a full suite of baths. They had every kind of top-flight nautical equipment too, some specially invented. In the polite version, these great ships were created so that crazy Caligula could partake in the rites of Isis. The better story says that they were intended for imperial orgies.

I made my way to the shore, where I found a man who claimed he had once worked aboard the vessels. The old whelk now spent his days dreaming of past glory. He had the sense to dream out loud, in order to receive charity from visitors. Even more bored than I was, in return for half a sestercius in a rather fine bronze bucket he just happened to have handy, he was happy to talk. He admitted he had stolen the bucket from on board. He spoke of triple lead-sheathing on the hull and heavy marble cladding on cabins and the poop; lion headed bollards; revolutionary bilge pumps and folding anchor stocks. He swore there had been rotating statues, powered by fingertip bronze bearings on secret turntables. He told me how these great ceremonial barges had been deliberately scuttled, once Claudius became emperor. I had heard about plenty of bad behaviour under Claudius, but the elderly ruler had at least claimed to clean up society. During his early days of promise, he had ordered the symbols of his predecessor's luxury and decadence to be destroyed. The Nemi barges were sunk. And then, like any King of the Grove knowing himself to be doomed, old Claudius settled down to wait for Nero's ambitious mother to serve him with a fatal dish of mushrooms. The nutty old emperor is dead; long live the even nuttier young new one.

The thought of the lost ships depressed me. I went back to walk in the woods. I wandered about despondently. Suddenly a man wielding an enormous weapon ran out from behind a nearby tree and rushed me. My assailant had a crude approach to fighting, but he was sturdy, fired up, and as he swung his big sword, I saw the panic in his eyes. I was in no doubt: his one idea was to kill me.

XLVII

I had brought my own sword, but could not immediately unsheathed it from its scabbard's cosy nook under my armpit. At first I was too busy dodging. There were plenty of trees to jump behind, but most were too slender to provide real cover. My opponent sliced through the sapling stems with all the hatred of a gardener slashing giant thistles.

Once I got my sword out, I was in a real predicament. I learned to fight in the army. We were taught to parry a stroke as violently as possible, jar the other man half senseless, then plunge in and kill him. I was happy to send this madman straight to the River Styx – but the investigator in me yearned to know first why the suicidal menace was attacking me. As we danced around and clashed blades, the effort seemed pointless. I was on the verge of ending it with one brutal stab through his ribs.

He was desperate. Every time I lunged forwards, he managed to stop me. I stabbed again: he accepted it like a gladiator who knows he won't leave the arena alive. Soon it was all defensive work; every time I attacked, he furiously protected himself If I slacked off, he should have gone for me with renewed vigour, but he seemed to have lost his initiative.

In the end I took a chance. I let my sword dangle from my hand, point down. I held open my arms, baring my chest for a death blow. (Believe me, I was out of range and I kept a good grip on the sword.) 'So kill me,' I taunted him. The moment seemed ageless and endless. Then I heard him whimper.

I whipped up my sword, jumped across the clearing, knocked him flat and fell on top of him. My sword point was pressing on his neck. I noticed it was slitting the complicated gold braid of a rather fine long white tunic – out of keeping with its wearer. He had a face like a milk pudding, with a dumpling where his nose should be and his body was degraded by rickets. His manner was an odd combination: bombastic authority mingled with sheer terror. The closest I had seen to this clown was a bankrupt financier when the bailiffs came – immediately before denial and self-justification set in. 'I know who you are!' the curious specimen gurgled. 'I bet you bloody don't… Who are you? Apart from a raving maniac?' 'I am nameless,' he wavered. This mission was full of spooks. 'Well that was an oversight on your father's part.' I released him abruptly and stood up, taking his weapon. I sheathed my own sword immediately, and stood back. 'Can I get up?' 'No. Stay there on the ground. I've had enough of you jumping around like a Spanish flea and trying to do me in.' 'I've been following you. I watched you searching -' 'I wasn't searching for you. Not unless you are a woman and extremely well disguised. Now listen to me. Whoever you think I am, my name – given to me by my mother, in fact, since my father was off buying a statue in Praeneste at the time – my name is Falco. Marcus Didius Falco, son of Marcus – a free Roman citizen.' He gasped. By then I thought he would. In a quieter tone I said encouragingly, 'That's right. Calm down; I am neither a slave nor a runaway. So I haven't come for you. You are the King of the Grove, I presume?'