King Charles I had been trying since the start of the Civil War in 1642 to find more troops. In 1643 he signed a 'cessation' with the Catholic Confederation of Ireland - an effective truce that allowed him to bring back the English regiments he had originally sent to Ireland after the rebellion of 1641. In November 1643, several of these regiments arrived in Cheshire, where a new field army was being formed under Lord Capell. Capell was replaced in December by Lord Byron, who had built his reputation as a hard-charging cavalry brigade commander in the king's Oxford Army. Byron took 5,000 men south and began clearing Cheshire of its Parliamentarian garrisons. Most surrendered quickly. At Barthomley Church on 26 December, however, the Parliamentarian garrison surrendered only after the Royalists lit a fire against the church doors to smoke them out - and at least twelve of the captured men, mostly local militia, were summarily executed afterward with Byron's approval. The killings became a propaganda gift to Parliament and stained the early phase of the campaign.

Nantwich was the last Parliamentarian-held town in Cheshire, garrisoned by 2,000 men under Colonel George Booth and well supplied with food and ammunition. It mattered to both sides: a centre of salt production, of leather tanning, of regional trade, and a town that Queen Elizabeth I herself had supported the rebuilding of after a catastrophic fire eighty years earlier. Byron besieged the town on 18 January 1644 and launched an assault that was beaten back at a cost of 500 Royalist casualties. Combined with losses from sickness, desertion, and the earlier Cheshire fighting, Byron's army had shrunk from 5,000 to around 3,800. The Sergeant-Major General, Sir Michael Erneley, had fallen ill. Byron continued the siege from his headquarters at Acton, a mile west of Nantwich. His regiments were quartered in a circle around the town, sheltering as best they could in farms and barns in a countryside covered in snow.

While Byron was besieging Nantwich, Sir Thomas Fairfax was in eastern England with his father, having been freed from the siege of Hull. His cavalry had ridden south to join Oliver Cromwell's Eastern Association horse, and together they had won several actions including the Battle of Winceby in October 1643. When Sir William Brereton's appeals for help reached the Committee of Both Kingdoms in late December, Fairfax was ordered west. On 29 December 1643, in bitter winter weather, he set out with 1,800 cavalry to cross the Pennines. The crossing was brutal - men and horses staggered through frozen passes - and when Fairfax reached Manchester, he found the infantry of the local Parliamentarian garrison so threadbare and demoralised that, according to contemporary accounts, he wept at the sight. Nevertheless, on 21 January 1644, he set out from Manchester with a combined force: 1,800 cavalry, 500 dragoons, 2,500 infantry, and several hundred poorly-equipped 'cudgellers' - civilian volunteers armed with whatever was to hand.

On 24 January, Fairfax brushed aside a Royalist screening force in Delamere Forest. Byron now had to decide: lift the siege, or fight Fairfax in the field with his depleted army. He chose to fight, and ordered his infantry and artillery to consolidate on the west bank of the Weaver around Acton, where the ground was drier. The next morning, the weather betrayed him. A sudden thaw set in. Snow ran off the Cheshire hills. The Weaver burst into spate, and the Beam Bridge - the main crossing north of Nantwich - was swept away along with a small ferry. Byron and his 1,800 cavalry were now on the east bank of a flooded river. To reach his infantry at Acton he had to march six miles north to another bridge at Minshull Vernon, then come back down the west bank. While he was making this circuit, Fairfax arrived in front of the Royalist position with the whole of his army. Colonel Richard Gibson, deputising for the ill Erneley, deployed four infantry regiments to face him, with the Royalist artillery massed in Acton churchyard.

Fairfax attacked at about two in the afternoon. The first Parliamentarian assault was repulsed by Gibson's men, but Fairfax's cousin William Fairfax led the cavalry around the Royalist right wing and forced it back. In the centre, Warren's regiment - the 'Irish' troops that the Parliamentarians had assumed would be Catholic and fanatical - broke and ran. Erneley's regiment retreated. Behind Gibson's position, Colonel Booth led a sortie out of Nantwich with 600 musketeers, overran Sir Fulk Hunke's regiment guarding the rear, and reached the Royalist artillery park in Acton churchyard. By half past four in the afternoon, only Gibson's and Sir Robert Byron's regiments were still fighting, the others having broken or retreated. They held briefly, then were overwhelmed. About 1,500 Royalists were captured. Many officers took refuge in Acton Church and surrendered on terms. Lord Byron, still cut off on the wrong side of the river, retreated to Chester with his cavalry.

The defeat at Nantwich destroyed the king's plan to base a new field army on the regiments returned from Ireland. Among the captured Royalist officers was Colonel George Monck - commanding Michael Warren's regiment - who later switched sides and would become one of the most important figures of the Restoration of Charles II in 1660. The townspeople of Nantwich named the day of their relief 'Holly Holy Day', supposedly because they wore sprigs of holly in their hats to celebrate. The custom survived in name only until the modern era, when the English Civil War re-enactment society The Sealed Knot revived it. Every year on the Saturday nearest 25 January, costumed soldiers march through Nantwich, fight a reenactment outside the town, and parade to Dorfold Hall on the road to Acton. The salt is still mined nearby. The river still rises in winter. The bones of the men who fell here lie under farmland, mostly forgotten, mostly unmarked - 1,500 Royalists captured, several hundred dead, and a king's plan washed away in a January thaw.