When Richard Hannay (Kenneth More) picks up a baby's rattle, that simple act sparks off a trail leading to espionage, intrigue and murder. The baby's 'nanny' is a secret service agent with orders to smash an espionage organization intent on smuggling plans of vital importance to Britain out of the country. Fearing for her life, the 'nanny' confides in Hannay who, whether he likes it or not, is now involved. When Hannay discovers her murdered in his flat, all he knows is that the brain behind the organization can be found in Scotland and the mystery is tied in with 'The 39 Steps'. Pursued by the police and members of the organization, Hannay boards a train for Scotland to try to clear himself of the murder charge by unraveling the mystery. In a music hall the high stakes for the country's safety are played out, and they learn the true meaning of those innocent-sounding, yet sinister words, 'The 39 Steps'.