Oldcastle is the eighteenth-century creation of the Naper family, who received parts of the older Plunkett estate after the Cromwellian wars. The most famous of those Plunketts was Saint Oliver Plunkett, the Roman Catholic Archbishop of Armagh — born in this area in 1625 and hanged, drawn, and quartered at Tyburn in London in 1681 on false charges of plotting against the king. He was the last Irish Catholic martyr executed in England. The town itself sits in the foothills of Sliabh na Caillaigh, the Hag's Mountain, and at the crossroads of the R154 and R195. Like so much of northwestern Meath it suffered terribly during the Great Famine of 1845–49 — the poorest tenants, holding the smallest plots in the most marginal land, were the worst hit, and the area lost much of its Gaelic-speaking population to starvation and emigration.

The Alien Restriction Act of 1914 was passed within twenty-four hours of Britain's declaration of war. It gave the government power to intern Austrian and German men of military age — anyone between seventeen and forty-two — on suspicion that they might return home to fight or stay in Britain as spies. The British War Office cast around for suitable buildings, and as one historian later noted, disused workhouses were ideal: they already had dormitories, kitchens, dining halls, washing facilities, an infirmary. Oldcastle's workhouse had stood empty for years. It was repurposed almost overnight. By the end of the war it would hold nearly six hundred men at a time, drawn from every German and Austrian and Hungarian community in Ireland — clergymen, jewellers, musicians, cooks, butlers, butchers. Most were civilians whose only crime was being born in the wrong country.

Conditions were not comfortable but they were not the conditions of a military prison camp either. Inmates were allowed to write and send two letters a week of twenty-four lines each. Parcels could be received. Visitors were allowed for fifteen minutes twice a month. The class divisions of Edwardian life were carefully maintained even inside the camp — wealthier inmates could rent their own rooms and hire poorer inmates as servants, because the British authorities believed it was not acceptable to put a docker in the same room as a doctor. One of the most prominent prisoners was Aloys Fleischmann, a Bavarian church musician and composer who had been the organist and choirmaster of Cork's Catholic cathedral. He wrote to his wife requesting three blankets and a pillow, a warm knitted jacket, waterproof boots, a wash bowl, a kettle, a mug, cutlery, tobacco, and books. The image of him sitting in a damp Victorian workhouse in Meath, asking for books, is one of the more humanising glimpses we have of what the camp was actually like.

On 13 April 1918, an anti-conscription rally was held in Oldcastle. The guest speaker was Arthur Griffith of Sinn Féin. Thousands attended, only three hundred metres from the camp. The prisoners climbed onto the roof of the workhouse to watch and listen. By that point the political ground in Ireland had shifted dramatically — the 1916 Rising had happened, the political landscape had hardened against British rule, and the speeches at the rally were openly nationalist and anti-British. Inside the camp, German prisoners watched Irish nationalists denounce the same British state that was holding them prisoner. It was one of the stranger tableaux of the First World War. The camp closed when the war ended. The prisoners went home or stayed in Ireland. The workhouse was eventually demolished, and Mellow's Park was built on the site by Meath County Council around 1950.

Today Oldcastle is a market town of around two thousand people, serving the surrounding farming country. Its industries lean towards furniture and bed manufacturing — Briody Bedding and Respa Bedding are major employers — and the Lithuanian community that arrived to work in those factories now numbers around two hundred. Three kilometres south, on the Hag's Mountain, lie the Loughcrew Cairns: a complex of Neolithic passage tombs built around 3300 BC, more than five thousand years ago, with chambers oriented to catch the sunlight at the spring and autumn equinoxes. They were already two thousand years old when Stonehenge was being completed. And in an oddity of modern life, the All Black rugby star Jordie Barrett spent fifteen months of his youth on a nearby farm — a small contemporary footnote to a town whose history runs back through internment camps and famine and martyred saints to the very edge of recorded Irish memory.