Tucked away in a secret location in the Rockies, Dr. Charles Forbin (Eric Braeden) has developed a massive computer system, dubbed "Colossus," that is supposed to ensure the nation's safety against nuclear attack. But when Colossus connects to a similar Russian computer, "Guardian," the intelligent machines begin conducting a private dialog. Nervous as to what they might be plotting, Forbin severs the connection, only to have Colossus threaten a nuclear attack if the link isn't restored.