Campbell was known to his Gaelic-speaking tenants as An Cù Ruadh - the Red Fox, after the colour of his hair and the reputation he had earned. To the Edinburgh authorities he was a loyal Whig and a hard worker. To the Stewart families about to lose their homes he was the face of a policy that was tearing apart the world they knew. Lochaber after Culloden was a wreck. The Jacobite cause had collapsed; clan chiefs had been executed or exiled; the estates of the defeated were being parcelled out under government commissioners; the bards spoke of the country as a body bleeding. Even the great Gaelic poet Alasdair MacMhaighstir Alasdair, in his satire An Airce, named Colin Roy Campbell - granting him, oddly, a certain respect among the Whig Campbells whom the poem otherwise damned. Campbell was a real man with a real family. He was laid to rest at Ardchattan Priory after a Reformed funeral. The bullet that killed him also killed any chance that the government would let his death go unanswered.

The chief suspect, Alan Breck Stewart, fled almost at once - and so the authorities turned to the man left holding the clan together. James Stewart of the Glens, known in Gaelic as Seumas a' Ghlinne, was the half-brother of the exiled chief and the de facto head of Clan Stewart of Appin until his nephew came of age. He was arrested two days after the killing. He was prosecuted by William Grant, Lord Prestongrange, before a court at Inveraray - the Campbell heartland - with a jury that was overwhelmingly Campbell. The defence had little to work with; the prosecution had even less, by some readings of the trial. A Glasgow lawyer studying the transcripts in 2008 would conclude there was 'not a shred of evidence' against him. None of that mattered in the autumn of 1752. James Stewart was convicted of being an accessory to murder. He was sentenced to hang.

On 8 November 1752 a special gibbet was erected above the narrows between Loch Leven and Loch Linnhe at Ballachulish - the place known in Gaelic as Caolas MhicPhadraig, MacPatrick's Narrows, near where the Ballachulish Bridge now lands on the south shore. James was led to it. Witnesses described him as a decent, God-fearing Highlander. He protested his innocence. He lamented, with terrible foresight, that people of the ages might think him capable of a horrid and barbarous murder. Then, before he was hanged, he sang. In the Gaelic tradition of exclusive psalmody in Reformed worship, he sang the metrical version of Psalm 35 in Scottish Gaelic - the psalm that begins 'Plead my cause, O Lord, with them that strive with me.' To this day in the Highlands, Psalm 35 is called Salm Sheumas a' Ghlinne, the Psalm of James of the Glens. His body was left hanging on the gibbet for eighteen months as a warning. Wind and rain pulled at it; as the corpse decayed, his bones were held together with chains and wire. When the family was at last allowed to bury him, his remains had to be washed before the Reformed funeral.

Almost no one then believed James Stewart had fired the shot. Almost no historian now believes it either. So who did? The most enduring answer comes from the oral tradition of Appin itself, where the name has been quietly passed down through at least twenty descendants of Clan Stewart over more than two hundred and fifty years. In 2001 Amanda Penman, an 89-year-old descendant of the Stewart chiefs, said openly what families had said privately: that four young Stewart tacksmen had planned the killing without James's sanction, held a shooting contest among themselves, and the best marksman - Donald Stewart of Ballachulish - had taken the shot. Penman said the actual shooter desperately wanted to turn himself in to save James, and had to be physically held down on James's own orders to prevent it. The historian James Hunter, in his 2001 book Culloden and the Last Clansman (later retitled The Appin Murder: The Killing That Shook a Nation), argued that James did order the killing, to defend his clan from the imminent clearances - and that even so, in the world he lived in, he was not acting ignobly. In 2016 two academics, Allan MacInnes and Mhairi Livingstone, suggested an entirely different culprit: Mungo Campbell, Colin's nephew, the only witness, the man who inherited the factorship, and the man who took charge of the investigation.

In 2015 the Scottish government declined to issue a posthumous pardon for James Stewart, and the official miscarriage of justice remains official. But the case never left the imagination of one Edinburgh writer in particular. Robert Louis Stevenson set Kidnapped in the immediate aftermath of the Appin Murder, with his hero David Balfour as accidental witness to the killing and forced into flight across the heather with Alan Breck. In the sequel, Catriona, David Balfour tries to clear James of the Glens and is kidnapped to keep him from testifying - held on the Bass Rock in the Firth of Forth until the trial is over. Stevenson, drawing on the same oral tradition Penman cited, depicted the killing as unauthorised, and the silence around the true shooter as a clan code of honour that no Stewart would break. Two and a half centuries on, that silence largely holds. The descendants of James of the Glens still gather to sing his psalm. The gibbet rotted away; the bridge replaced it. But the Highland wood where Colin Roy Campbell fell is quiet now, and what happened there is still, in some hard old way, the property of the people who live with it.