A two-bit criminal takes on the Mafia to avenge his brother's death. Earl Macklin is a small time criminal who is released from prison after an unsuccessful bank robbery only to discover that a pair of gunmen killed his brother.

A fleet of Martian spacecraft surrounds the world's major cities and all of humanity waits to see if the extraterrestrial visitors have, as they claim, "come in peace." U.S. President James Dale receives assurance from science professor Donald Kessler that the Martians' mission is a friendly one. But when a peaceful exchange ends in the total annihilation of the U.S. Congress, military men call for a full-scale nuclear retaliation.