Lincolnshire Police are investigating a robbery in Pinchbeck, which saw four men enter a Spar shop, spray a liquid onto a member of staff, and steal cash and cigarettes from the tills.
The robbery took place on Knight Street at around 9.40pm on Thursday, November 17.
The suspects all managed to escape and officers believe they got into a vehicle near to the store.
The employee who was sprayed suffered minor injuries.
All four men were wearing dark clothing and had their faces covered.
Officers are speaking to witnesses and a forensic examination of the store is being conducted.
Detective Inspector Dave Rimmer from South Holland CID said: “This is a serious offence which will be fully investigated but thankfully attacks of this nature are uncommon in this area.
“I urge that staff in late night convenience stores to be extra vigilant. If any staff have seen any activity which they regard as suspicious they should contact the police and let us know.”