LAPD cops Jack Traven and Harry Temple rescue a group of executives
trapped in a sabotaged elevator, thus foiling mad bomber Howard Payne's
ransom demands. In retaliation, Payne sets a new challenge for Traven: a
bomb on a city bus which will arm itself when the bus reaches 50 mph, and
which will explode if the bus drops below that speed or if any of the
passengers try to escape.