A thick fog has blanketed much of Britain now for forty-eight hours, debilitating air and rail traffic. At London Airport at Heathrow, no flights are coming in or going out, but the British Overseas Airways Corporation (B.O.A.C.) and the other airlines are transporting people stranded at the airport by bus to other airports where flights are operating. Elderly and belligerent Miss Cynthia Beeston (Dame Margaret Rutherford), who believes the world should revolve around her and her alone, is able to commandeer one of the B.O.A.C. buses to take her and three other passengers - unaware ingénue Janie Grey (Belinda Lee), staid Edward Schroeder (George Coulouris), and milquetoast Henry Waterman (Toke Townley) - to Blackbush Airport. A last minute addition is suave Peter Jones (Terence Alexander), a pilot. Pretty and no nonsense Lee Nicholls (Petula Clark), a flight attendant, serves as the attendant on the bus. However, they may not get to Blackbush as their driver, exasperated and bumbling Percy Lamb (Frankie Howerd), who has had enough problems working his way around London Airport in the fog, has never driven to Blackbush. What most of them are unaware of is that a robbery of two hundred thousand pounds sterling worth of gold bars had just occurred at the airport prior to them leaving, those gold bars which the robbery mastermind, nicknamed "The Banker", had stashed on their bus. The Banker is likely one of the seven of them, which places the lives of the other six in danger if The Banker is discovered and cornered. When the Police discover where the gold bars are, their problem is not only trying to speak to anyone, but the unknown Banker via the airline's speaker system to the bus, but trying to locate where the bus is, which is lost in the fog.
—Huggo