The man giving the orders was Seán Mac Eoin, a 27-year-old blacksmith from Ballinalee whose forge had become an unlikely command post for the IRA in County Longford. He had built the flying column the previous autumn, twenty-one volunteers who had already killed four Royal Irish Constabulary men over the course of 1920. The British response came in November: a company of the Auxiliary Division — ex-army officers, well paid, well armed, raised specifically to break men like Mac Eoin. By January the Auxiliaries had been reinforced. By February, Mac Eoin had decided to strike first. He chose Clonfin because the road narrowed there and the cover was good, and because the lorries from Granard would have nowhere to go but forward.

The ambush opened with rifle fire from the embankments above the road. The Auxiliaries were veteran soldiers and they fought back hard, turning what Mac Eoin had hoped would be a short engagement into a sustained gun battle. Four of the IRA volunteers worked their way around the flank and shot the Auxiliary commander, Lieutenant Commander Francis Craven, dead in the road. With Craven gone, the remaining policemen surrendered. Four Auxiliaries had been killed and eight more lay wounded across the roadside. The IRA collected their weapons — rifles, revolvers, ammunition — the entire point, in a war where firepower was always scarce.

What happened next is why people still argue about Clonfin a century later. Mac Eoin walked among the surrendered Auxiliaries and congratulated them on the fight they had put up. He stopped his own men from beating the prisoners. He had water brought from nearby farmhouses for the British wounded, who lay bleeding on the February ground waiting for help that would take hours to arrive. Months later, when Mac Eoin was captured at Mullingar railway station and put on trial for his life on charges of murdering an RIC inspector, three of those same Auxiliaries crossed the country to testify on his behalf. They told the court martial what the blacksmith of Ballinalee had done for them at Clonfin. He was sentenced to death anyway, and was saved only by the July truce that ended the war.

There is no story of the Irish War of Independence that ends cleanly, and Clonfin is no exception. In the days after the ambush, British forces returned to the surrounding townlands and burned a number of houses and farms in reprisal. They shot dead an elderly farmer in the process. The North Longford Flying Column went to ground and did not attempt another major attack for the rest of the month, partly out of caution and partly because Mac Eoin's arrest in March took the heart out of the local campaign. A memorial stands at the ambush site today, and in 2010 a ceremony was held there at which speakers urged remembrance not only of the IRA volunteers but of the Black and Tans and Auxiliaries who died — an unusual gesture in this part of Ireland, and a direct echo of the way Mac Eoin himself had treated his enemy on the road that February morning.

The land around Clonfin is the soft drumlin country of north Longford, low rounded hills cut by hedgerows and pasture, the kind of landscape that looks too gentle to have ever held an ambush. The townland itself is barely a place by modern standards — a stretch of road, a few farms, the memorial. Ballinalee, where Mac Eoin's forge once stood, lies a few miles to the west; Granard, the historic Norman motte town, rises to the east. From the air on a clear day you can pick out the line of the old road and the gap in the hedges where the lorries came through. Most travellers pass without noticing. The names of the twenty-one men of the flying column — Brady, Callaghan, Conway, Cooke, Farrelly, Finnegan, Geraghty, Gormley, Hourican, Hughes, Kenny, Lynch, McDowell, Moore, Mulligan, Reynolds, Sexton, Sheeran, Duffy and the two Bradys — are inscribed on the memorial. So are the Auxiliaries.