Miss Frontier Mail

The deputy station master (Ishwarlal) at a railway station is murdered by a man in a mask. In the scuffle his mask comes off and one of his hench-men sees his face. They escape from there just before the station master Maganlal (Master Mohammed) arrives who handles the knife which has been used to kill the deputy. The police appear and arrest him for the murder. His daughter Savita (Nadia) and son Jayant (Jaidev) get the news by a wire sent by their uncle, Shyamlal (Sayani Atish).

Nadia a.k.a. as Frontier Mail is fond of hunting, playing tennis and racing fast cars while Jayant is an amateur film maker. Soon Jayant and his friend (Munchi Thoothi) get involved in the villain's antics as they manage to film him and his gang readying to blow up a bridge.

The masked man dynamites the bridge as he's been contracted to do so by a man who wants to promote his airline business. There is also a gangster's moll Gulab (Gulshan) who is romantically linked first with Shyamlal and then with Kishore (John Cawas). Gulab later reforms and sides with Nadia and her brother in hunting down the masked man. Sunder (Sardar Mansur), is the son of the head of the railways authority. He becomes infatuated with Savita and rushes to help her.

They are involved in several chases culminating in a fight scene on top of a speeding train where Savita fist-fights the gang alongside Sundar. She lifts some of the men and hurtles them down the tracks. It's finally revealed that the masked man who calls himself Signal X is none other than Savita's uncle Shyamlal.