
When Hank tries to send a message by Morse code, the voices tell him it is useless and that the team will vanish along with the island, after which there will be further attacks on mankind. After more of the island falls into the ocean, Dale and Karl find oil in a fissure and attempt to locate its source, but Karl accidentally steps on the trigger for the electronic ray and is killed. Later, while Hank attempts to build a new radio transmitter, Martha gently rebuffs his romantic interest by explaining that she is committed to Dale. After Hank uses the specimen to demonstrate that the crab can be destroyed electronically, he devises an electronic ray to kill the creature. From a photograph Karl took of the second crab, Martha deduces that it is pregnant and the team decides that it must be killed. Karl also believes that the crabs are deliberately destroying the island by causing the earthquakes. Back at the laboratory, Karl theorizes that not only have the giant crabs been created by radiation, but also that they are assimilating characteristics of the human victims they are eating, absorbing their brain tissues and minds. Karl takes a specimen claw from the crab, but as they leave, another giant crab appears and Deveroux's voice warns the scientists against trying to destroy him. When Karl, Dale and Hank enter the cave, they are attacked by a giant crab, which although impervious to gunfire and grenades, is killed when a falling rock penetrates its brain. The following night, Deveroux again speaks to them, telling them that something remarkable has happened to him and invites them to see for themselves by joining him and Jim in the caves. The others are wakened by his screams, then hear his voice, but find his room empty.

Deveroux goes there and is killed when a giant claw grasps him by the neck. Later that night, after Fellows and Sommers are murdered in their tent on the beach, Deveroux is awakened by their voices telling him they have found Jim and instructing him to meet them at the rim of the pit. The group returns to the caves to search for Jim, but a severe earthquake triggers a rockfall that results in Deveroux losing one of his hands. After the others fail to find Jim, they return to discover that the laboratory has been deliberately destroyed and their radio transmitter wrecked.

When Dale enters the laboratory, he is attacked by a giant claw, but escapes. While Dale and Martha return to headquarters, the others take a different route to the bottom of the pit through caves along the beach. Later, the others find Martha, and Jim calls to them from the pit to tell them he has a broken leg. Jim decides to descend to the bottom via a rope, but loses his grip when an earthquake strikes, causing him to fall to the bottom as Martha faints. Outside, Martha bumps into Jim, who has also been summoned, and together they follow the voice to the newly formed pit. That night, Martha is awakened by a voice identifying itself as McLean and begging for help. When they return to the surface and head back to the laboratory, Karl and Jim show them a fifty-foot-deep cave-in on the trail they had taken to the beach. The next day, Martha, a marine biology expert, begins her underwater studies and is joined by boyfriend Dale. In the team's laboratory, Karl reads the journal and learns that McLean had noted a possible increase in size of the island's creatures due to atomic radiation. After the new group experiences an earthquake and avalanche, Quinlan and his crew leave to fly back to their base, but the plane explodes on takeoff, killing the crew. Quinlan, the naval officer assigned to transport the team, was a member of the search party that attempted to find the earlier group, but found only the journal left by leader McLean. As supplies are being unloaded, a seaman falls overboard and is decapitated by something in the surf.


This team replaces a previous research expedition, which the navy believes disappeared during a typhoon. James Carson botanist Jules Deveroux demolition experts Ron Fellows and Sam Sommers and electronics specialist Hank Chapman. The other members of the team are biologists Dale Drewer and Martha Hunter geologist Dr. Karl Weigand, to a remote Pacific atoll to study the effects of atomic fallout from nearby H-bomb tests. Navy seaplane delivers a team of scientists, led by nuclear physicist Dr.
