The story begins on the Sea Girl, just after departing San Francisco, where Steve Costigan notices John Zachary Grimes, a reserved new crew member from Kentucky. Grimes quickly proves his strength and unwillingness to be bullied by defeating Olaf Ericson, a veteran crew member, in one hit after a disrespectful remark.

Despite Grimes's impressive display, he remains a loner, gaining respect but not companionship from the crew. His interactions with Costigan are tense and filled with mutual tests of strength and character. Both men are formidable fighters, but while Costigan enjoys the sport of it, Grimes fights only when provoked, focusing on decisive and permanent victories to avoid further confrontation.

The ship approaches Singapore, where Costigan is scheduled to fight in a highly anticipated match against Kid Reynolds. However, as the crew disembarks, Costigan receives a suspicious note, luring him to the Dragon Shop under the pretense of meeting a woman. There, Grimes confronts him, revealing it was a ruse to discuss concerns about the upcoming fight. Despite initial anger, Costigan listens as Grimes hints at possible foul play intended to disrupt the match and tarnish Costigan's reputation.

Before Costigan can learn more, Grimes secretly drugs him, intending to protect him from participating in the possibly rigged match. Costigan wakes up too late to participate in his fight and discovers that Grimes has taken his place, losing on purpose to avoid scandal. Costigan, furious and confused, confronts Grimes outside the venue, leading to a brutal fight where both men express their frustration and strength.

After a long and punishing duel, McPartland, the fight promoter, finds Costigan and explains the situation: Grimes stepped in to protect Costigan's reputation from a setup orchestrated by corrupt gamblers, including Slippery Steen, who had planned to drug Reynolds to ensure a Costigan victory and subsequent scandal. Realizing Grimes's actions were to preserve his honor and that of the Sea Girl, Costigan reconciles with Grimes, recognizing his integrity and sacrifice.