When experimental drilling on the pacific sea-bed breaks through the earth's thin mantle, vast quantities of nitrogen, trapped for untold millions of years, are released into the atmosphere. As a result, the oxygen in the air becomes dangerously diluted. Whole areas of America are thrown into chaos as the inhabitants literally fight for breath. Two men and two girls put to sea in a yacht in a desperate effort to escape the terror, but terror, in a different and no less deadly form, pursues them relentlessly.