The Folly of Conceit unfolds the story of a young boxer, Patrick O’Hanlon, whose life is a series of dramatic turns shaped by ambition, vanity, and the eventual realization of his follies. Born in Ireland but raised in North Carolina, Patrick grows up amidst a community of Irish and Scottish immigrants, where his penchant for fighting and physical strength become evident. Disinterested in farm work and influenced by his Danish seafaring ancestors, Patrick ventures into the sea at fifteen, only to find his true calling in boxing at eighteen, thanks to a passenger, Mr. Harmer, he meets aboard.

Quick to rise in the boxing world, Patrick's success is meteoric, but it's also the breeding ground for his conceit. Despite Mr. Harmer's guidance, Patrick's vanity makes him susceptible to flattery and bad influence, notably from a man named "Slick" Baden. A turning point comes when Patrick, enticed by Joan Cromwell, a wealthy socialite, neglects his rigorous training regimen for the company of Joan, leading to indulgence and deviation from his disciplined life.

The narrative peaks when Patrick, drunk and misled by Joan, wakes up in disarray, jeopardizing his upcoming fight against Jack Penhryn, a formidable opponent. His condition deteriorates as he resorts to extreme measures to make weight, undermining his physical fitness and mental acuity. Despite a promising start to the fight, Patrick’s lack of conditioning and overconfidence unravel, marking his downfall.