Jan Letterman, Barbara Wilkin, is the personal assistant to the wealthy, aging actress Laura Winters, Rita Morley. When Laura hires pilot Grant Murdoch, Byron Sanders, to fly her from New York to Provincetown, Massachusetts, a sudden storm forces the group to crash-land on a secluded island. On this lonely shore, they encounter Prof. Peter Bartell, Martin Kosleck, a marine biologist with a German accent who has carved out a life of quiet seclusion among the rocks and tides.
The island holds a disturbing mystery: a string of strange skeletons wash ashore—first human, then fish—while the surrounding waters teem with a glowing microbe that mercilessly devours flesh. Bartell reveals a chilling past as a former US Government agent sent to Nazi Germany to recover their scientific data; his mission and linguistic skills made him the ideal candidate for a dangerous plan. He has been studying these microbes with an eye toward cultivating a terrifying army of flesh-eating creatures that can strip away skin in a matter of seconds.
A beatnik named Omar, Ray Tudor, joins the stranded group after a shipwreck, bringing a rough-edged practicality to the tense dynamics. With the plane now gone and the island cut off from the world, the castaways—and Bartell—realize they have become potential meals for the ravenous monsters lurking in the surf and seaweed.
Bartell's controversial experiments take a dramatic turn when he engineers a high-voltage solution, using a battery system to flood the waters in an attempt to kill the creatures. He explains that his goal was to weaponize these organisms, turning them into a tool of destruction. Yet electricity does not kill them; it fractures the microbial swarm, causing countless smaller microbes to fuse into a single, larger organism. This accidental evolution forces the survivors to rethink their approach as the threat grows even more formidable.
As the days unfold, the survivors learn a crucial detail about the creatures: they crave flesh but not blood. In every instance where remains include blood, the monsters are vulnerable. The group experiments with this vulnerability, and the realization becomes key to their plan for survival. Bartell posits that directly injecting hemoglobin can neutralize the creatures, offering a potential counterattack against the threat they face.
With time running out, a bold move is made: a sustained electrical shock is applied to the surrounding waters, coaxing the dispersed microbes into a single, colossal organism. The struggle that follows is brutal and tense, culminating in Bartell’s death just as Grant Murdoch takes decisive action to destroy the final creature. In the end, Murdoch and Jan Letterman manage to escape the island together, leaving the island’s deadly secrets behind as the sun sets on their narrow odds of survival.
