Stan Butler, a bus driver for the Town & District bus company, grows anxious about the overtime that helps his family buy big items like a washing machine, especially as the firm contemplates rectifying its staffing shortage.
That fear becomes reality when the company decides to revoke a long-standing rule that prevents women from being employed as bus drivers, a move that disappoints both Stan and his long-time colleague and friend, Jack Harper.
To help cover expenses, his sister Olive Olive Rudge is encouraged to join the company's canteen; after a rocky start, she and her husband, Arthur Rudge, discover that Olive is pregnant, which leads to her losing her job and forcing the Butler family to return some of the items they can't pay for.
Meanwhile, Stan's attempt to retrieve something of Jack's from a woman he's been seeing backfires when he ends up demolishing a telephone kiosk and a bus shelter while trying to avoid her jealous husband.
Blakey, the inspector, informs Stan that he must take a driving test on a bus skid pan to keep his job. Stan engineers a cheeky reversal when he begins the test with Blakey still aboard, turning the situation in his favor and passing the test.
With the threat of women drivers looming over their carefree lifestyle, Stan and Jack decide to sabotage the plan by making the new group look bad, starting with small pranks. Olive's fear of spiders becomes part of their scheme as they plant them in the cabs to unsettle the drivers; they escalate to lacing the women's tea with a diuretic after learning what it does during Olive's pregnancy, forcing many toilet breaks and delaying several routes.
Meanwhile, the company orders diversion signs to steer buses away from roadworks. The duo repurpose these signs to create more chaos, including a false diversion that sends a woman driver onto a motorway, drawing scrutiny from Blakey.
A mishap on the way to the hospital results in the bike and sidecar breaking, but Olive still reaches the hospital and gives birth to a baby son, disrupting the household further. Though their sabotage seems successful when the company announces it will no longer employ women drivers, Blakey rehires them and splits Stan and Jack onto different routes.
Stan's luck changes when a new attractive clippie, Sandra, is assigned to his route. The pair enjoy a new, mischievous rapport as they dream up further pranks on Blakey, including knocking down a sign that provokes a reaction from the inspectors.
With the route ahead, Stan heads off on his shift, buoyed by companionship and a renewed sense of freedom, ending the tale on a cheeky note as he heads toward the next stop.
