"Nights at the Circus" is a fantastical tale set in the late 19th century, centering around a trapeze artist who claims to be a swan princess with wings. A journalist is intrigued by her story and joins the circus to uncover the truth. As the troupe travels from London to Siberia, the journalist becomes increasingly enchanted by the strange world of circus performers and his relationship with the trapeze artist deepens. The book explores themes of love, freedom, and the blurred lines between reality and illusion.

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.