A teenager wearing a Halloween mask robbed a newsagent's shop armed with a large knife, police said.
The Strathclyde force is trying to trace the youth who targeted McGuigan's Newsagent in Dalry, Ayrshire, at about 1200 GMT on Friday.
He threatened the 60-year-old shop assistant, but fled when he was challenged by the woman.
The teenager did not escape with any money, but did steal some goods from the store in New Street.
Police said the shop assistant, who had been alone in the store, was unhurt but had been been left shaken by the incident.
The robber was male, about 16 years old, 5ft 7in tall, and was wearing a light blue hooded top with a darker blue hood and light jogging bottoms.
The youth, who spoke with a local accent, was also wearing a white Halloween mask to cover his face.
Police are studying CCTV footage and have appealed for information from anyone who was in the area at the time.