Workaholic Dr. Jeremy Stone has to initialize the top-secret national emergency plan he devices in a facility also planned by him when a mysterious, viciously rapid disease strikes a Utah backwater, actually after a small meteorite strike. His small team of scientists and specialized military doesn't realize one of them is in league with the infamous general George W. Mancheck, whose top-secret project is somehow entangled with the plague.
The plague-bringing 'meteorite' is found, actually a military satellite from general Manchek's top-secret project. Dr. Jeremy Stone's team works out the virulent organism found on it has 'alien' properties, yet its anatomy suggests lab-design. Tests on it and survivors study reveal radiation would only strengthen it, just before an atomic bomb is to be dropped, but the pilot is affected by the now bird of prey-spread organism.
Dr. Jeremy Stone's team desperately examines the staggeringly rapid and radical mutations of the Andromeda organism, which thus obtains carriers and eats trough anything, even the pilot's breathing pipe so as to accidentally cause the atomic bomb to be dropped after all. At first sight purely academic speculation ranging from philosophy to astro-biology combined with observing the temporary survivors yield crucial findings of the sulfuric acid-based enemy. The organism is constructed, communicating like an ants army. Pountless detail in its design puzzles them, until ...
Dr. Jeremy Stone's team successfully tests the bacteria-based cure, then decides to destroy all samples, fearing for communication, while racing against time to produce enough while the pest spreads. The military-political conspirators however blackmail a member to keep one, which frees itself and thus starts the auto-destruct, which proves extremely hard to shut down. Meanwhile escaped reporter Nash is chased by troops and the cover-up continues after the organism is eradicated.