The narrator and his fiancée, Gloria, are adventurers flying from Manila to Guam when they crash into the sea near a mysterious, fog-shrouded land. They swim to shore and find themselves on a beach bordered by towering black cliffs, creating an ominous and confining atmosphere. Gloria's intuition suggests a forbidding presence, which she cannot articulate but feels deeply.

As they explore the beach, the narrator notices Gloria's increasing discomfort and strange remarks about transmitting thought waves, hinting at a psychic disturbance. Despite her fears, they decide to separate briefly as the narrator goes in search of a way to climb the cliffs. During his exploration, he encounters driftwood and tracks that unnervingly resemble those of giant crabs.

Returning to the spot where he left Gloria, the narrator finds only her severed hand, setting off a visceral, heart-wrenching reaction as he faces the brutal reality of her death. Overcome with grief and fury, he dedicates himself to avenging Gloria. He soon discovers the island's inhabitants: gigantic, intelligent crab-like creatures far superior in intellect but alien in their understanding and empathy.

The crabs, realizing the narrator's presence and potential threat, confront him in a chilling encounter that reveals their intellectual and psychic superiority. Despite this, the narrator finds his physical prowess an advantage in this alien conflict. As he adapts to his role as a predator, he uses his strength and primal instincts to survive and hunt the crabs, driven by a deep-seated need for vengeance.

The ongoing battle takes a toll on him, both mentally and physically, as he wages a guerrilla war against the crabs, hiding and striking opportunistically. His skirmishes are marked by brutal encounters and narrow escapes, highlighting the extreme psychological and physical demands of his crusade.

As he prepares for a final assault on the crab city, located in the higher cliffs, the narrator reflects on the nature of his conflict with the crabs. He contemplates the inherent cruelty in nature's order, where different species are pitted against each other in a relentless struggle for survival. His narrative ends with a resolute march towards a suicidal battle, determined to cause maximum destruction to the crabs before his inevitable death.