Billy Byrne is a low-class American born in Chicago's ghetto. He grows up a thief and a mugger. "Billy was a mucker, a hoodlum, a gangster, a thug, a tough." He is not chivalrous nor kind, and has only meager ethics - never giving evidence against a friend or leaving someone behind. He chooses a life of robbery and violence, disrespecting those who work for a living. He has a deep hatred for wealthy society. He trains as a prizefighter but cannot stop drinking.

When falsely accused of murder, he flees to San Francisco and is shanghaied aboard a ship. Ironically, enforced sobriety, brutal ship's discipline, and productive work improve him. The ship's secret mission is soon enacted - the hijacking of a specific yacht to take a millionaire's daughter, Barbara Harding, for ransom. Billy Byrne brutally beats her suitor, Billy Mallory, leaving him for dead. "He knew that she looked down upon him as an inferior being. She was of the class that addressed those in his walk of life as 'my man'."

After Barbara confronts him and calls him a coward, a change begins in Billy Byrne. He saves the life of one kidnapper, Theriere, rather than letting him be washed overboard, though he cannot fathom his own reasons. After a terrible storm, the ship is damaged and only makes it to land with Billy's help at the wheel. He rescues Barbara from the wreck and brings her ashore. Barbara is kidnapped by headhunters descended from medieval Japanese. Byrne and Theriere race to rescue her from the daimyo's hut in the middle of the village.