This novel centers around a young woman, Milly Theale, who is terminally ill and wealthy. She becomes the object of a conspiracy by two other characters, Kate Croy and Merton Densher, who are in love but too poor to marry. Kate manipulates the situation so that Densher becomes close to Milly, intending for him to marry her and inherit her wealth when she dies. However, Densher eventually falls in love with Milly, leading to a complex triangle of love, deceit, and moral ambiguity.

This novel delves into the captivating and secretive world of 18th-century Italian opera, focusing on the lives of castrati, men who were castrated as boys to preserve their soprano or alto vocal ranges. It follows the journey of a young nobleman who, after being brutally castrated, embarks on a path of revenge, transformation, and eventual acceptance as he becomes a celebrated opera star. Through his eyes, the reader is immersed in the opulence and cruelty of the era, exploring themes of identity, sexuality, power, and the complex interplay between pain and beauty. The narrative weaves a rich tapestry of historical detail, emotional depth, and lyrical prose, capturing the human struggle for self-discovery and artistic expression.

The novel is a sprawling epic that spans the period from the 1893 World's Fair to the years following World War I. It follows the stories of several characters including the anarchist Traverse family, a group of balloonists, a detective, and a mathematician. The book explores themes of anarchism, capitalism, and technology, and incorporates elements of science fiction, adventure, and historical fiction. It is noted for its complex structure and dense, multifaceted narrative.