MacRory's St Patrick's Day sermon was not unusual in its substance. The Catholic Church across Europe was alarmed by the rise of communism in the wake of the Russian Revolution, and Irish bishops had been preaching against it for years. What was unusual was the timing - a national feast day, with crowds already on the streets - and the specificity of the targeting. Connolly House was a known address, a small office above a shop, sheltering an organisation that the historian Emmet O'Connor estimated had fewer than seventy-five members in Dublin and only about twenty active ones by the following year. The communists were politically negligible. They were targeted because they were available. A march that began as a religious procession from the Pro-Cathedral became a hunt for a specific door, and a few hundred people made it clear, in the space of a short walk, that the line between sermon and crowd action could vanish faster than anyone in the Pro-Cathedral had perhaps intended.

The first violence happened away from the main target. On Aston Quay, on the south bank of the Liffey, a smaller crowd identified two men they believed to be communists and beat them. The Irish Times reported that the mob attempted to throw both men into the river and that Garda officers had to wade in physically to rescue them. The phrase 'throw them in the Liffey' had real meaning - the water at Aston Quay was tidal, cold, and deep enough to drown a man at high tide. The two men survived. Whether they were actually communists or had simply been mistaken for them in the heat of the moment was never established, and in the chaos of that night it probably did not matter. The crowd had decided, and the river was right there.

By 10.30 pm the main body of the mob had reached Connolly House. According to Eugene Dowling, one of the defenders inside, the attackers broke through an iron gate into a furniture store next door before forcing their way into the back of the building. Several of the people sheltering in Connolly House were armed. They opened fire as the mob came through the door. No deaths were recorded but the gunfire bought the defenders the few minutes they needed to do what they did next, which was extraordinary. They climbed through an interior doorway into the upper rooms of the Italian fish and chip shop next door. The shop was open. The owner served them. Dowling's account, recorded decades later for RTÉ radio, has them quietly sitting down at the chipper's tables and eating a meal while the mob next door wrecked their headquarters, never realising that the people they were trying to burn out were calmly working through a portion of cod a wall away.

The standard later telling of the riot - that this was a poor, lumpenproletariat mob whipped up by clerical rhetoric - has been challenged by more recent historians, including Donal Fallon, who points out that much of the crowd appears to have been respectably middle-class. The 1930s in Ireland were the decade of the Blueshirts, the quasi-fascist movement led by Eoin O'Duffy, and of the broader anti-communist mobilisation that swept much of Europe. Catholic Action groups, professional associations, and rosary processions blended into political action in ways that look unfamiliar now but were normal then. The Communist Party headquarters was burned out a second time before the year was over. By 1934 the party in Dublin had effectively ceased to function, its membership reduced to a few dozen committed activists meeting privately. The riot did not kill anyone, but it destroyed something all the same: the assumption that a public political space existed for ideas the Church had named as enemies.