The Hardy Boys have come to Chicago with the father to attend a meeting of computer experts at the Evanco building. But suddenly, without warning, the 120-story skyscraper is turned into a tower of terror. A gang of gunmen invades the offices, snatches an attractive young college woman, and disappears into the night!

Her name is Sarah Evans, daughter of the rich and reclusive owner of Evanco, J.P. Evans, and her kidnapping is the key to a global conspiracy of computer destruction. The world's most powerful computers have been turned into long-distance time bombs, and Frank and Joe are racing the clock -- both to save Sarah and defuse the ultimate high-tech weapon!