A Viking space capsule suddenly and unexpectedly returns to Earth from an explorative trip to Mars,, a journey it should not have been able to make on it's own. It brings with it an armour clad alien that's hell bent on finding and sending back information in preparation for the invasion of Earth.

NASA scientists take the alien to a lab for intensive investigation, but are hindered by the army who seize control of it and the space capsule. When the alien inevitable escapes, the killing begins and the army desperately tries to recapture or destroy it. Failure will mean the destruction of all life on Earth and the end of the human race.