A 57-year-old woman was hit in the face as she tried to get into a taxi in Market Place, police have said.
She was dragged around the back of the vehicle by another woman outside the library at about 1am on Sunday November 11.
She suffered injuries to her face.
The attacker was with two men who then left the area.
She was described as being white, 5ft 5ins tall, in her 20s and of large build.
She had short straight mousy hair and was wearing a dress.
Witnesses or anyone with information should call police on 101.