In 1929, a local scientist delivers a mysterious present to newlyweds, with the note "Don't Open Till Doomsday" on it. The groom Harvey Jr. disappears shortly thereafter, and his bride Mary waits over 35 years until a new set of newlyweds comes along.

Alien parasites plan the conquest of Earth by attaching themselves to the spinal columns of men in power. They recruit disaffected loners to spread their infection... unaware that one of the loners is a government agent sent to infiltrate them.