In 1870, in the town of Mamaroneck, New York, on the Long Island Sound, managers are hiring recently arrived Italian immigrants for renovation work at cheaper rates than the Irish-Americans already in town. Some Irishmen are laid off, and animosity grows. Fights break out throughout the summer.

On August 13, some of the Irish workers notice the Italian laborers are getting paid before them. After some drinking, they pick a quarrel with some Italians, crowding against them and hurling denigrating epithets. A young Irishman is seriously — if not fatally — stabbed and violence erupts. The two mobs hurl stones and other debris at each other. Knives are freely wielded.

Newspaper accounts claim the deaths of two Irish and two Italian workers, but the numbers are never confirmed.