Montrose crossed into Scotland with his small force of about 1,300 , soon depleted as the Cumberland and Westmorland militiamen deserted in droves because they objected to serving outside their own immediate area. Montrose arrived at Dumfries with only a few hundred men, as 2,000 promised reinforcements from Ireland were not forthcoming and in the face of a Covenant army, Montrose had to abandon his guns and retire to aid Royalist efforts in the north of England. On 6 May his patent as Marquis arrived from the King, and three weeks later (aided by guns from the Newcastle garrison) he captured Morpeth. He was strengthening the defences of Newcastle when he was called to assist Rupert, but before he could do so, Royalist fortunes in the north had been decided in battle.

It was commonly thought that the final charge at Marston Moor had decided the business of the kingdom. Perhaps it had, for the north was lost to the King. Rupert gathered what horse he could and departed, leaving the veteran governor of York, Sir Thomas Glemham, to hold out for as long as he could; he capitulated on 16 July. The Marquis of Newcastle, having expended a fortune and fought nobly for his king, quitted the war altogether, taking ship at Scarborough for Hamburg rather than 'endure yc laughter of ye Court' ". With him gone, there was noone left capable of rallying Royal support in the north.

Charles I was in pursuit of Essex when he learned of the catastrophe. Given his letter stressing the value of York, it was difficult to understand why such disaster had occurred, but it probably added urgency to the King's campaign to destroy Essex. With the north gone (though Glemham's garrison was to be allowed to march out unimpeded to Chester), a victory in the south was imperative to attempt to redress the balance. Additional pressure might be put upon the Scottish alliance if Montrose could cause sufficient trouble in Scotland to compel the recall of their army from England, but when he met Rupert at Richmond two days after Marston Moor, Montrose was able to extract nothing from the despondent Prince, though he begged for 1,000 horse to take into Scotland.

In early July Alasdair Macdonnell landed in Argyll- shire and attempted to rally support from the west Highland clans, but met with limited success due to the predominance of the Covenant forces. The saturnine Presbyterian Archibald Campbell, Marquis of Argyll, raised his clan and destroyed Macdonnell's ships, leav- ing him isolated. Macdonnell managed to recruit 500 Gordons, but wrote in desperation to try and contact Montrose, who at this point was roaming the area of Perth and Dunkeld endeavouring to drum up support. Montrose and Macdonnell united at Blair, where Montrose unfurled the Royal standard. Montrose's force comprised only the Irish 'brigade', if it may be so termed, and some 1,200 Highlanders, the latter ill- disciplined and armed with bows and broadswords, but his opponents were not much better off - Highlanders and largely untrained local levies. Three Covenant armies faced him, Lord Elcho in Perth, Argyll's Campbells in the west and Lord Burleigh at Aberdeen, so Montrose set about defeating Elcho before he could be joined by Argyll. Montrose's small force met Elcho fled; Montrose's whole force followed and utterly (7,700 strong, though 500 of his archers had changed sides the previous day) at Tippermuir on 1 September. Short of ammunition, Montrose arrayed the Irish in three ranks (instead of six) to enable them to deliver one massive volley which he hoped would be enough; the Atholl clansmen he commanded in person had only stones to throw. It was more than enough, for Elcho's horse charged, was devastated by musketry, broke and routed the remaining Covenant troops.

Perth surrendered immediately, but Montrose lost almost all of his army save the Irish, the Highlanders following tradition and, after winning a battle, re-turning home with their loot, a problem which was to dog Montrose for the remainder of his career. Not daring to await the junction of Argyll and Burleigh, Montrose set off to defeat the latter, recruiting some 75 invaluable horse on the way. On 13 September he routed Burleigh before Aberdeen, the indifferent Covenant levies proving no match for the Irish brigade, Still with insufficient strength to meet Argyll, Montrose rc- tired, leaving a remarkable success behind him having defeated two and evaded one of the three armies send to annihilate his small force.

In the Highlands, Montrose rallied support from those clans with old enmity towards the Marquis of Argyll's Campbell clan, and was supplemented furtherby the defection from Argyll Of 15o Gordon horse. Taking the war to Argyll's homeland, Montrose pillaged the Campbell capital, Inverary, and created such consternation that some of Leven's army was drawn northwards out of England, thus achieving Montrose's primary objective. William Baillie, one of Leven's generals (aided by Urry, who had deserted the King before Second Newbury) commanded a force at Perth, Argyll headed the main body of his army, the Earl of Seaforth led another corps at Inverness, and a Covenant garrison held Aberdeen. To prevent the union of Argyll and Seaforth, Montrose decided to attack the former by a hill route, difficult enough in summer but almost impossible in mid winter, surprising and routing Argyll's army at Inverlochy. The Campbell clansmen received no quarter in payment for years of oppression; as the Gaelic poet Ian Lom Macdonald wrote,

No harp in the highlands will sorrow for you; But the birds of Loch Eil are wheeling on high, And the Badenoch wolves hear the Canteron's cry - 'Come feast ye! come feast where the false-hearted lie!"'

For Montrose's loss of about a dozen men, it was claimed that around 1,500 Campbells were killed in the pursuit or drowned in Loch Linne and Loch Eil.

Having recruited his army to about 2,500 foot and 200 horse, Montrose intended to strike at the Lowlands, but as before, with each victory, his Highlanders melted away home with their booty, forcing him to retire north to reorganize. Before going, Montrose sacked Dundee, but whilst his troops were looting he learned that Baillie's Covenant army was but a mile (1.6 kilometres) away. Commanding a rearguard Of 200 sober Irish, Montrose managed to get the remainder of his drunken, disorganized troops away before Baillie arrived. Baillie divided his forces in an attempt to trap Montrose (always a hazardous manoeuvre against so skilful an adversary), Urry with four good Lowland regiments and some mediocre levies (totalling about 4,ooo) being tempted to assault Montrose's 1,000 Irish foot and 650 Gordons at Auldearn, two miles (3.2 kilometres) east of Nairn, on 9 May. When the Gordon horse led a counterattack against Urry's regulars the Covenant army was overthrown, with only Urry and too horse escaping after a 14-mile (22.5-kilometre) pursuit.

Only in Scotland was the King's party having any success, and that due entirely to the efforts of one remarkable general. After Auldearn, Montrose consistently outmanoeuvred a harrassed Baillie, whose plans were interfered with constantly by advisors attached to his army by the Committee of Estates, the ruling Covenant body. Another army was also formed around Perth, commanded by Lord Lindsay. Having sent away Alasdair Macdonnell to recruit, Montrose had only O'Cahan's regiment and loyal Highlanders when he encountered Baillie at Alford on 2 July. Spurred on by his travelling committee, Baillie attacked unwisely and came to grief as Lord Gordon, commanding Montrose's horse and incensed at the sight of captured Gordon cattle with Baillie's army, charged prematurely and, followed by the rest of the army, routed the Covenant force, though Gordon himself was killed in the fight. Baillie's resignation was refused for the second time and he was given a new army, mostly untrained levies, and, to ensure disaster, another travelling committee under Argyll. Engaging Montrose at Kilsyth, midway between Stirling and Glasgow, on 15 August, he met with no more success than before; Montrose broke Baillie's centre whilst containing his right, then turned upon that and destroyed the army. Argyll fled as far as Berwickupon-Tweed and others fled to Carlisle.

Scotland was a more fertile ground for Charles' hopes, and on 5 February 1649 a proclamation was issued acknowledging his succession as Charles 11 and lamenting the 'wicked and trayterous murther wee doe from our soules abominate, and all parties and consenters thereunto'; on 22 February Montrose was appointed the King's Captain-General in Scotland with instructions to raise a loyal army. Rather than accept the severe terms put to him by a Scottish delegation which visited him in Holland in 1649, however, Charles prevaricated in the hopes of success in Ireland. When there was no longer an alternative, he entered into new negotiations with the Scottish Commissioners at Breda. The ruling Scottish Committee of Estates proposed terms which even Argyll considered too strict, but Charles was encouraged by William 11 to agree, and on 1 May 1650 signed the Treaty of Breda. By this he undertook to impose Presbyterianism upon England, to outlaw Roman Catholicism, to acknowledge the Scottish Parliament and renounce the arrangements with Montrose and Ormonde, in return for an invitation to be crowned in Scotland and to have the Engagers' rights restored to them. Probably neither side intended to abide by these agreements; Charles must have been unenthusiastic about the religious strictures, and the Scots wished only to use him as a figurehead to help further their own ends.

Before the treaty was signed the last acts of a great and gallant general had been played out in Scotland. Montrose, in his last heroic bid in the Royal cause, landed at Kirkwall in the Orkneys on 23 March 1650. With him were some 5oo Danish and German mercenaries, 1000 local recruits, a troop Of 50 horse, old Royalists and mercenaries, and the practiced turncoat Urry, once more a Royalist. Montrose's small force - of negligible military value for the Orcadians were totally untrained - awaited the expected Royalist rising among the clans. It never came, and Montrose was crushed by the local forces from Inverness at Carbisdale on 27 April, the Orcadians fleeing without striking a blow. The mercenaries and horse put up a good fight but were overwhelmed.

Montrose and Urry were executed in Edinburgh in the following month. Montrose's last words concerned his King and country; his late master, who 'lived a saint and died a martyr', and his present sovereign, in whom 'never any people ... might be more happy in a king''. His dying declaration, 'May Almighty God have mercy on this afflicted country", might well have applied to the whole of the island, for when the king for whom Montrose had died entered Aberdeen en route to his proclamation as king in Edinburgh, having repudiated the principles for which his general had died, he passed through the city gate over which still hung a dismembered arm of the great Marquis.