A teenager flagged down a bus and tried to rob the driver at knifepoint.
Wiltshire Police said the offender had been at a stop on Blackberry Lane in Potterne, near Devizes, at about 2120 GMT on Sunday.
After boarding the empty bus, he produced a knife and demanded money.
The driver refused and the would-be robber ran down Blackberry Lane. Det Con Simon Childe said: "This was a shocking experience for the driver."
The offender is described as white, aged between 16 and 19 years old, about 5ft 7in tall and slim.
He had short blond hair which was brushed forward.
Any witnesses are asked to contact the force.