ATTACK OF THE CRAB MONSTERS

A group of scientists and their support crew of five sailors land on a remote island in the Pacific Ocean. They are searching for a previous expedition that disappeared without a trace, and to continue research on the effects of radiation from the Bikini Atoll nuclear tests on the island's plant and sea life. The scientists, led by Dr. Karl Weigand, include geologist James Carson and biologists Jules Deveroux, Martha Hunter, and Dale Drewer. Their party also includes technician and handyman Hank Chapman.

Soon after their arrival, a sailor, Tate, falls in the water and is killed, his decapitated body floating to the surface. Two sailors are left behind to guard the explorers, while the others, led by Ensign Quinlan, attempt to return to the mainland, but their seaplane inexplicably explodes. The scientists are unable to report what happened due to a storm, so they decide to stay on the island and continue their research. They read journal entries written by the previous scientific team, which mention killer worm creatures. Martha and Dale later go scuba diving. That night, Martha hears "McLane", leader of the previous expedition, calling out to her. Carson descends into a pit that opened up during an inexplicable earthquake and falls, losing his footing.

The current expedition learns to their horror that the earlier group had been killed and eaten by two mutated, intelligent giant crabs, who have absorbed the minds of their victims and can speak telepathically in their voices. Members of the current expedition are being systematically attacked and killed by the monsters, which are now invulnerable to most standard weaponry because of their cell structure mutations.

The remaining scientists finally discover that both giant crabs are the cause of the ongoing earthquakes and landslides on the island; they are slowly destroying the island, reducing its size, by undermining it with tunnels. The scientists turn their attention to a way to stop the mating pair of monsters from reproducing. They are able to kill one of the giant crabs in a cave when their placed explosive detonates, shaking loose an overhead rock that crushes the head of the monster.

As the island continues to fall away into the Pacific, and after barely escaping from their collapsing laboratory building, the surviving trio of Dale, Martha, and Hank finally meet the remaining intelligent giant crab, Hoolar, who speaks to them via telepathy. Hoolar vows to go to the mainland with her fertilized eggs when the island is gone (and the three humans are dead) to feed upon even more people, absorbing those minds in the process. Hank then sacrifices himself by bringing down an electrically-charged broadcast tower directly on top of the giant crab, electrocuting the monster and her unhatched brood. Dale and Martha embrace on the small portion of what remains of the once large island.

The surviving trio confronts the last giant crab, Hoolar, who threatens to bring her fertilized eggs to the mainland. Hank sacrifices himself by electrocuting the monster and her brood, allowing Dale and Martha to escape.

The film concludes with a desperate act of self-sacrifice as Hank uses an electrified broadcast tower to destroy the final mutant crab and her potential offspring, preventing the threat from spreading beyond the island. This resolution reinforces the B-movie trope of science gone awry being ultimately contained by human bravery, with the survivors narrowly escaping annihilation.