Workers at a fish and chip shop in Caistor were threatened with an air rifle during an attempted robbery on Friday evening.
At around 8:04pm, a man entered The Fish and Shop in the Market Place and demanded staff hand over cash while waving the weapon at them.
But the employees bravely refused and the offender fled the scene.
Nobody was injured in the incident but staff are said to be shaken by the experience.
The man is described as white and aged in his late 20s to mid 30s. He was 5’7” to 5’10” tall, of a slim to medium build, clean-shaven and with no noticeable accent. He wore a green or brown hooded top with the drawstring pulled tight so that only his face was visible.
The air rifle was partially wrapped in what may have been a waxed jacket or dark coat.
If you have any information, contact investigating officers DS Dave Harrop or DC Jim Wilson of Lincs Police on the 101 non-emergency number.
Or call Crimestoppers anonymously on 0800 555111