The O'Leary family travels to Chicago to seek their fortune, with mom working as a washerwoman to support her sons. Brothers Power and Ameche become power-broking rivals and when mom comes to break up a brawl between the two, she neglects to properly restrain the family cow. This leads to the great Chicago fire of 1871, supposedly started when the cow kicks over a latern and sets the barn ablaze. The city burns down in a spectacular 20-minute sequence. Based on the story "We the O'Learys" by Niven Busch.