'Is she fact or is she fiction?' is the burning question on the lips of Londoners who see Fevvers perform on stage at the Alhambra in 1899.  In her unique acrobatic act, she unfurls her wings and glides at a leisurely pace from floor to trapeze - a genuine, fully fledge bird woman.  Young American journalist Jack Walser is determined to discover just how genuine she is, and the novel opens as he interviews her for his series on 'Great Humbugs of the World'.

Fevvers' story takes in her upbringing in a brothel, and her pubescent experimentation with flight.  When the brothel's madam died, she tells Walser of her time in a freak show, of being sold to the lecherous Christian Rosencreutz, who aims to sacrifice her in a ritualistic rite of May.

After her escape, Fevvers joins Colonel Kearney's Imperial Circus, and as the novel's main timeframe begins she is poised to depart for Petersburg and Japan.  Walser, intrigued, joins the circus as a clown in order to follow her.  In Petersburg the circus opens in triumph, but a current of discord is gradually exposed.  The Strongman's woman leaves him to dance with the Princess of Abyssinia's trained tigers.  The Educated Apes break their contract and depart; the Charivaris, a family of acrobats outshone by Fevvers, attempt to murder her and are dismissed.  As the master clown, Buffo the Great, drinks himself into oblivion and a jealous tigress is shot onstage, Fevvers accepts an invitation from the wealthy Grand Duke on the eve of the circus' departure from Petersburg.

The Grand Duke attempts to imprison Fevvers in his collection of automata, but she escapes through a tiny train within a Faberge egg, which transports her to the Trans Siberian Express where the remainder of the circus awaits.  The train heads east, but crashes in the wilderness when a troop of outlaws blow up the track.

The members of the circus are captured by the outlaws, who believe that Fevvers is engaged to the Prince of Wales and that Queen Victoria will pardon them in return for her release.  The clowns dance the outlaw camp into oblivion, and the dwindling remnants of the circus are freed; all except Walser, who was left unconscious and without his memory after the train crash and rescued by a shaman who believes his language is that of dreams.  In the wilderness, the circus troupe discover their inner selves and separate, leaving only Fevvers and her foster mother Lizzie seeking for Walser.  

Fevvers and Walser are reunited at last in the shaman's village on New Year's Eve.  They recognise their mutual love as the old year fades into the new, and Fevvers' laughter heralds the coming century.