Upon awakening, he encounters a distressed French dancer named Diane, who reveals herself to be trapped on the island by the feared Shark Murken, a man of power, a former fighter turned smuggler and tyrant, who wishes to marry her against her will.

Driven by a combination of chivalry and attraction, Costigan agrees to a perilous bargain: he will fight Shark Murken in a boxing match for Diane's freedom. Murken, proud of his pugilistic prowess, accepts the challenge, setting the stage for a brutal and decisive confrontation. The fight is a testament to Costigan's resilience and determination, unfolding under the sweltering heat and the watchful eyes of the island's assorted denizens. Despite being poisoned by his own cornerman, Costigan triumphs, knocking Murken out and seemingly winning Diane's hand.

However, in a twist, it is revealed that Diane's affections lie with another—Armand, a young man she had loved all along. Diane's plea for Costigan's help was a ruse, a desperate strategy to use his fighting skills to liberate both herself and Armand from Murken's grasp. The story concludes with Costigan, battered but undaunted, facilitating the couple's escape to a new life, while he returns to the Sea Girl, his true love, ready to face whatever the next port has in store.