An earthquake shatters a peaceful Los Angeles morning and opens a fissure deep into the earth, causing lava to start bubbling up. As a volcano begins forming in the La Brea Tar Pits, the director of the city's emergency management service, working with a geologist, must then use every resource in the city to try and stop the volcano from consuming LA.

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.