The Turnberry Bond was signed at Turnebyry in Carryke, on the eve of St. Matthew; the 20th of September, 1286.
The historical event involving the Turnberry Bond is better known as the Turnberry Band. For some strange reason, the event that was the signing of the Turnberry Bond instead became known by a collective noun for its group of signatories. According to logic, the bond of agreement that was signed shouldn't and couldn't have been called the Turnberry Band. It was a bond and it was known, at least in Scotland, as a bond – the Turnberry Bond. The band of rogues that signed it could've been given various names and calling them the Turnberry Band is one of the more generous options.
The prime movers in the signing of the Bond were
the Bruces, father and sons. The father was Robert de Brus VII, the 5th Lord of Annandale, known as the 'Competitor'. The sons were Robert de Brus VIII, the then Earl of Carrick, and his brother, Richard de Brus, uncle of the future king, Robert the Bruce, which latter was all of twelve in 1286.
That's important, because Wikipedia’s article on the Turnberry Band has a note referring to the 'fact' that “Bruce and his like-named son, witnessed a charter of MacDonald to Paisley Abbey, sometime in the reign of Alexander III” and goes on to suggest that “This charter is probably the earliest historical record of the man who would later become Robert I, King of Scots.” Well, obviously that's incorrect as the Bruces referred to are clearly the grandfather and father of the future king, rather than being Robert the Bruce and his father.
Two further illustrations of the note being erroneous are that: (i) Robert I, King of Scots, didn't become Earl of Carrick until 1292, when his father's wife died and the title passed to the son; and (ii) the father of Robert I didn't become the 6th Lord of Annandale until either: (a) 1292, when his father renounced his title rather than swear fealty for it to Balliol; or (b) 1295, when his father died.
The remaining members of the Turnberry Band were the Dunbars (Patrick de Dunbar, Earl of Dunbar, and his three sons, Patrick, Master of Dunbar, John and Alexander); three Stewarts (Walter Stewart, Earl of Menteith, and his two sons, Alexander and John); two more Stewarts, one a Guardian who was also High Steward of Scotland (James Stewart, the Guardian, and his brother, John Stewart of Jedburgh); the two Ulstermen (Richard de Burgh, Earl of Ulster and Thomas de Clare, Lord of Thomond); and the Islesmen (Aonghas Mor mac Domhnaill, Lord of Islay, and his legitimate son, Alexander Og).
A reproduction of the Turnberry Bond appears in Latin in 'The Red Book of Menteith' by William Fraser (Edinburgh, 1880) and here's the key extract: “Bond by... [the aforementioned, whereby they engage to] ...adhere to the noble men, Sir Richard de Burgh, Earl of Ulster, and Sir Thomas, Lord of Clare, in all their affairs, and with them and their accomplices to stand faithfully in resistance against all their adversaries, without prejudice to the faith of the Lord the King of England and without prejudice to the faith of him who in the Kingdom of Scotland, by reason of the blood of the Lord of happy memory, Alexander, King of Scotland, last deceased, shall obtain and succeed according to the ancient customs of the Realm of Scotland approved and customary until now.”
According to Michael Brown in 'The Wars of Scotland, 1214-1371', the purpose of the Bond was the obvious one of curtailing Hebridean support for the Ó Neill and Ó Domhnaill dynasties, enemies of the Earl of Ulster, through an alliance of Scottish and Anglo-Irish nobles. Brown's interpretation is that, despite links to the Stewarts and Bruces, the need for a bond indicates that the loyalties of Angus Mor of Islay, head of Clan Donald, were a wee bit suspect. Alexander of Argyll, on the other hand, had a link to John Comyn of Badenoch, but because he had been the agent of Alexander III in the Isles, he was somehow less suspect. Anyhow, getting the Comyn's brother-in-law on-side wouldn’t have pleased that faction.
Michael Penman in his book, 'The Scottish Civil War', suggests it would be a mistake to underestimate the Bruces' ability to rouse significant opposition to Comyn dominance in the south west and, indeed, throughout Scotland at that time. Ostensibly, what Penman means is that, in addition to the obvious, knowledge of the Bond's existence must have given food for thought to many potential territorial rivals of the Comyns and their allies i.e., friends and potential allies of the Bruces. The Bond served as Bruce propaganda.
If you like, the ambitions of the elder Bruce, the 'Competitor', can be deduced from the Bond, although it's was nothing like a blatant “up yours” to the Comyn-led Guardians of Scotland. But if you take into account the actions of the Bruces after the Bond was signed, it's not a stretch to see it as the 'Competitor' rallying support in preparation for a tilt at the crown. Alan Young, in 'Robert the Bruce's Rivals: The Comyns, 1212-1314' and referencing Barrow, says that the fact that such a pact of family and factional, if not national intent, could take place and that a Guardian was involved, was certainly an ugly defiance of the “community of the realm.”
In relation to the Bruces activity, Brown states that the 'Competitor' took the field “in force of arms with banners displayed” with Carrick, his son, and captured the Royal castles of Wigtown and Dumfries, and also Lady Dervorgilla's stronghold at Buittle. Thereafter, the Bruces wreaked considerable damage in the south-west. Young offers that, because of the fear of further violence and Bruce's actions in the south-west in late 1286, the Guardians issued a brieve asking for the host to be on twenty-four hours' alert.
The Bruces actions certainly seem to have been targeted at upsetting Comyn dominance of the Guardianship and the government of Scotland, which the 'Competitor' undoubtedly felt necessary, because the exclusion of the Bruces was likely to threaten any future claim of theirs to the Scottish crown. Ultimately, the Bruces failed to win widespread support at that time. Perhaps they overestimated the extent of that significant opposition. Between 1286 and 1289, the Guardians stood firm against the Bruces' challenge and their 'little war' ended with them handing back the castles they'd taken and swearing fealty to Margaret, the Maid of Norway.