Quan is a humble London businessman whose long-buried past erupts in a revenge-fueled vendetta when the only person left for him to love – his teenage daughter – dies in an Irish Republican Army car bombing. His relentless search to find the terrorists leads to a cat-and-mouse conflict with a British government official whose own past may hold the clues to the identities of the elusive killers.

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.