Leo ordered a taxi to drive him from his splendid Glasgow apartment to the railway station and spent the minutes it took to arrive checking – for the seventh time – that the ashes in the grate were dead, gases were turned off and electricity plugs were disconnected.

The driver was an odious, high-pitched little character, who quickly broached the subject of immigration and spat a racist word into the conversation. Leo requested that he refrain from such language, then, before the man had a chance to respond, pretended to busy himself with his mobile phone, during which he made great play of jotting down the cabbie's name and number in his notebook. Upon arrival at Queen Street station Leo paid him exactly – no tip – and took inordinate pleasure in counting out a stack of grubby coppers as part of the fare.

He purchased his ticket and stowed himself and his considerable quantity of monogrammed luggage in the foremost carriage of the Oban train, which was empty of other passengers. He rubbed his gnarled hands together as he settled down at a seat with a table, and produced a felt-lined box containing a little gold-rimmed glass with harp and shamrock motifs etched on it, and a silver flask with beautiful Celtic knotwork relief. He polished the glass with a napkin, filled it with a shot of Scotch from the flask, took a swig, and settled himself down for a snooze. After adjusting his velvet-lined slumber mask, he fell instantly into an uncomfortable sleep.

A slight jolt of the train is an explosion of light within Leo's dimmed consciousness, followed by a split-second rush of the shockwave tearing the air as it rushes towards him.

He jerked, both in his mind and in the physical world, to avoid the impact, and snapped out of the uncharacteristically brief vision. He found himself blinded by the blast. Panicked, he reached for his eyes and felt the slippery texture of his mask. He tore it off to reveal yet another level of altered reality: massive patches of blond sand deposited upon the embankments of the West Highland Line. He blinked several times, unable to compute this weird phenomenon. Was he still dreaming? Was he locked within an endless nightmare of hallucinations? Then he realised – it was snow. Of course – the Scottish Highlands in winter. Snow.

Leo then endured a brief crisis of hypochondria brought on by the fact that his left leg had gone to sleep during his fitful nap. Having convinced himself that he was about to suffer a fatal stroke, he popped a Mogadon, mumbled a prayer, and urgently proceeded to jot down the hymnal for his funeral Mass, regretting having put the task off thus far. The onus was unsurprisingly on the side of gravitas – Mozart and Fauré – but the sentimentalist in him couldn't resist 'Hail, Queen of Heav'n, The Ocean Star' and then 'Be Still, My Soul' for the exeunt to the hearse. That'll have them weeping in the aisles, he mused morbidly, before realising that the feeling had by now returned to his lower limb and that the magic bullet had calmed his anxiety with its soporific charm. Despite that, he wondered with trepidation what the turnout would actually be at his funeral; he had fallen out with so many friends and associates over the years. He tried to number those who loved him, and pictured one of those melancholy, pitifully attended affairs: a rainy November day, a few old acquaintances shaking hands in the porch of a cold church and murmuring uneasy platitudes for the deceased, politely promising to meet up for a drink one of these days, a white lie at the ready to excuse themselves from attending the wake. Too much gravy and not enough meat in the steak pie.

Leo popped a consolatory segment of Fry's Orange Cream into his mouth, put his earphones in and switched on the radio, but the mountains blotted out the signal. Suddenly, he regretted his parsimony in not having invested in an iPod. 'Join the twenty-first century,' he could hear his friend Stephanie Mitchell, a procurator fiscal, tease. His phone vibrated on the table with a text alert. Coincidentally, it was from Stephanie: 'I told DI Lang 2 xpect u at Loch Dhonn.'

Bloody decent of her.

His thoughts turned to the murdered girl. The picture the police had released to the media was one of a pretty, petite brunette wearing a graduation gown, proudly clutching her nursing certificate, smiling out at the world, full of anticipation and hope. He read the newspaper story for the tenth time:

Police have named the Loch Dhonn village murder victim as 22-year-old Helen Addison. The body of Miss Addison, a recently qualified district nurse, was found early on Thursday morning by a local man. She had several knife wounds. It is not yet clear whether Miss Addison had been sexually assaulted. Police said they are questioning Miss Addison's boyfriend Craig Hutton, 21, at an unnamed Glasgow station and that Mr Hutton was 'voluntarily helping them with their inquiries'.

Speaking for the Addison family, Mrs Grace Dunn, the victim's aunt, said: 'Helen was a lovely young woman, a beloved and valued daughter, sister, cousin, niece and friend, who had returned to her home community of Loch Dhonn as a newly qualified nurse. Her career choice was testament to her caring, compassionate nature. Words cannot begin to describe the devastation Helen's mum Lorna, dad Stuart and brother Callum are experiencing at this time. Her wider family, numerous friends and everyone whose lives Helen touched have been profoundly shocked by this wicked act.

'Someone, somewhere must know who did this. Perhaps they suspect a loved one. No matter how hard it seems I urge you to go to the police. Whoever is responsible may do it again unless you act. Please, you have the power to stop another family going through this hell.'

Leo thought about how the remains of poor Helen Addison would soon be ensconced within an obscure little patch of Scottish clay. And how brutally the months and years would rush by for the people who had loved her, denied her presence at their triumphs and festivities as she was now denied her own triumphs and festivities. The pang of guilt endured at each mundane task, as though performing it in her absence was in some small way a betrayal, an act of forgetting her. And as they speculated forevermore upon what she would have been, the lettering on the gravestone would quickly fade with lichen and the weather, and the rest of the world would march on, blind to the void of her absence.

He recalled his conversation with Stephanie, which had ended in discord when she had visited him three days ago.

'I might as well tell you: I'm going up there.'

'Where?'

He had gestured towards the day's newspaper, which lay front page up on the chaise longue.

'Why?'

'I had a vision. If I get to the scene of the crime I might be able to work out who the bastard is. Being there might stimulate my senses.'

'When are you going?'

'I've yet to decide. I fear if I arrive upon the locus too soon after the event the police may spurn my advances.'

'You likely won't be made welcome, regardless of how long you delay it.'

He had gazed out of the window, watching the rain whirl in the orange glow of the streetlamps and fall upon the riverbank across the road. Drops tap-tapped irregularly on the pane. She was right, of course; he probably wouldn't be welcome. Furthermore, he mused, it takes a lot of pluck, or perhaps foolhardiness, to approach the authorities with information pertaining to a case. He knew from bitter experience that knowledge of a crime (pertinently, knowledge bestowed by a vision) tends to place the bearer under suspicion. But he felt he had no choice. He could not bear a repeat of the tragedy that had occurred when he hadn't spoken up.

Leo disembarked at the quaint railway station at Fallasky, which was approximately eight miles from the village of Loch Dhonn. He was the only passenger to get off. He waited for the locomotive to pull away, then teetered across the line with his cases. A minicab was parked near to the station house. Leo approached it hopefully, and the driver, an affable-looking, slightly unkempt man with oily black hair who wore sports slacks, a tired, brown leather blouson jacket and NHS spectacles, cheerfully announced he was indeed for hire, got out and stowed the luggage in the boot. Leo climbed into the rear and tried to disguise his distaste for an unhygienic faux-sheep's-wool throw draped over the seat.

After a while they were on a single-track road, snaking through wooded countryside towards their destination. At one point they passed a stand of pines upon some raised ground to Leo's right, and he could catch tantalising glimpses of the silver surface of Loch Dhonn flashing through the gaps between their poker-straight trunks. Further on, the branches of a hundred snow-coated firs protruded over the road like robed arms, their ghostly fingers pointing. For some of the journey they were stuck behind an HGV rig with no trailer, which laboured up a series of narrow inclines, its airbrakes hissing violently. The rural taxi driver remained patient, evidently a more amiable species than his urban cousin.

'Terrible business up here,' he ventured.

'Terrible, terrible,' agreed Leo.

'Are you with the papers?'

'No. I'm here on holiday, believe it or not.'

'Oh.'

Leo was seized by the sudden realisation that the driver might take him for a ghoul. 'I had already booked it. I'm up for the fishing, as a matter of fact,' he blurted, before realising that this claim was fatally undermined by his conspicuous lack of angling gear. Silence descended for the remainder of the journey, and Leo decided to browse a local guidebook he spied tucked in a storage net attached to the rear of the passenger seat.

Loch Dhonn was a narrow freshwater lake, situated just below the immense diagonal fissure that splits Scotland in two. Running for thirteen miles in a jagged slash roughly from south to north-northeast in Argyll, it was over three hundred feet deep in parts and approximately a mile in width. The northern reaches were dotted with several small islands, some of which bore evidence of prehistoric and medieval settlements. At the northernmost point sat a Munro, Ben Corrach, a giant, bleak sentinel which rose to three thousand seven hundred feet and watched over the loch's entire length. The scattered settlement that took its name from the loch was small, with little more than seventy permanent residents, although this was boosted by the transient population of the Loch Dhonn Hotel, which dominated the place. Loch Dhonn village was one of fewer than a dozen hamlets sprinkled down the loch's eastern shoreline, which boasted a slightly better road than the facing bank. Apart from the hotel, built around an ancient hunting lodge in the 1840s during the grouse-shooting boom, there was a general store, a small community hall rebuilt in the 1960s, a Presbyterian kirk and, just to the north, a lovely Episcopalian church, as though plucked from a green and pleasant English dale and plonked down like a little curio within this majestic and savage valley.

They passed through some lower, sheltered ground: an expanse of squat trees, naked but for moss, ivy and flaking bark, their gnarled branches reaching out like the limbs of prehistoric beasts petrified instantly by some sudden catastrophe. One particularly ancient dying specimen bore a likeness to a dragon, which had been accentuated by an imaginative local wit painting on a sinister pair of red eyes. It seemed to guard the northern extremity of the village. They crossed a little stone humpback bridge, negotiated a final, twisting climb, before descending into Loch Dhonn itself.

The original buildings clung mainly to the east side of the undulating road, which at this point sat well above the water level and was set quite far back from the loch itself. The clachan was permanently shadowy due to the high arbour above the road and the steep law to the east side. Other, modern abodes, some of them luxurious and in the Scandinavian style, had been established amid the young birchwood and perennial shrubbery below the road, weekend homes for well-off Glaswegians, Leo guessed. Between them and the lochside was another half mile of land, mostly drab blanket bog, the rushes withered and brown, punctuated by the odd skeletal tree, like death's crooked hand, or where the soil was loamier tracts of meadow, some of it pleasantly stocked with mature woods. Leo consulted the little book again: the land above the road, which didn't rise much above five hundred feet, was largely part of the local estate. Cutting through this was Glen Fallasky, which ran roughly north-east towards the railway village where Leo had disembarked.

The hotel's imposing Scots Baronial exterior was constructed from pale grey stone. The three-storey building had a grand portico, several craw-stepped gables, two turrets and a thin tower, all topped with steep conical roofs. The taxi couldn't pull up at the front doors because the driveway was choked with various police and media vehicles, and a brewery lorry obstructed a little lane which ran along the side of the building. Leo was deposited beneath a leviathan Wellingtonia, upon a forlorn little area of raw earth, which was the shade of cinnamon and dotted with patches of snow and ice. He paid the driver and was duly handed his luggage.

He surveyed the anaemic landscape, the colour bled out by winter's death. 'Et in Arcadia ego,' he murmured. Yet, despite the land's dun seasonal garb there persisted a certain brutal handsomeness to the place. Leo gazed over towards the loch. A quintessentially Scottish scene. A ruined castle, wreathed in mist and clad in masses of gushing ivy, sat upon the largest island of a little archipelago. Spirals of vapour smoked off the braes on the facing bank, which were bearded by snowy brakes of native timber and serried ranks of commercially planted conifers. A mile to the south, the height of these slopes crested to almost that of a Graham then abruptly plunged, cloven by a great pass, a gateway to the west coast. A thin cataract tumbled in silvery slow motion from this distant promontory. Momentarily, the sun blinked from behind a cloud, drenching the crown of Ben Corrach in light as though it had been painted in oils, and making the water which sat in its lap sparkle. Leo felt a surge of joy in his lungs as he descended the muddy incline towards the hotel.

He tottered awkwardly with his heavy luggage, taking care not to slip, watched by two amused uniformed policemen who were glad of this mildly entertaining interlude to the boredom of guarding the crime scene perimeter. Leo was aware of their stares. He was used to people finding humour in his eccentric attire and gait, but he prided himself on paying it no heed whatsoever. He was more concerned by what lay behind the young coppers in the near distance: an extensive thicket of rhododendron from within which sprouted the branches of bare elms and rowans. It seemed chillingly familiar to him. A sense of foreboding welled up within him.

At that very instant the beast, sitting alone in the darkness of its cellar, amusing itself with thoughts of its dire deed, opened its eyes wide, as though disturbed by an awareness of Leo's arrival. His coming had already been foretold in code by its dark ancestor on the other side, by means of the strange runes. It would observe its adversary carefully, and consider what steps need be taken.

Nothing was off limits.

The hotel lobby was splendidly furnished and presented a predictable Highland interior. Some logs burned cheerfully in the grate, dwarfed by a magnificent mantelpiece constructed from carved, varnished maple. A couple of newshounds sat in the lounge area, chattering loudly and unselfconsciously to their editors through their mobile phones. Leo walked to the unattended reception desk. He placed his cases down and pinged the bell with his open palm. The cold air from outside lingered in the folds of his coat like an energy. As he waited he noted a just-about passably decent rip-off of Landseer's Monarch of the Glen.

'Do you like the painting, sir?' came the voice of a man who had arrived behind the counter.

Leo turned to face the speaker, a friendly-looking fellow in his seventies. His socialist sensibilities were always offended by being addressed as 'sir' by an older person.

'It has real character,' replied Leo diplomatically.

'It is by a locally based fellow. They have a kind of artistic community, just down the road.' He reached out his hand. 'Bill Minto,' he said. 'You must be Mr ...?'

'Moran,' replied Leo as he shook the hotelier's hand. 'Leo Moran. I telephoned earlier.'

'Of course,' said Minto, checking the book. 'Apart from a few of the newspaper chaps you're our only new guest this week. As you can imagine.'

Leo raised his eyebrows in acknowledgement.

The man glanced at Leo's hands and felt a pang of sympathy. The melted skin reminded Minto of the burns on his torso, which he had sustained on active service.