A woman was threatened at knifepoint outside Matalan in Wellingborough town centre.
The victim was walking towards Aldi at about 9.25pm last Friday (August 11) when she was approached by a male who then produced a knife and threatened to kill her if she failed to hand over her bag.
A police spokesman said: “In the struggle which followed, the victim fell to the floor after grabbing the knife, ending up with the blade in her hand still holding her bag.
“The offender pulled the bag causing it to come away from the handles and he then ran off in an unknown direction.”
The offender is described as 5ft 3in and he wore a black hooded top, with the hood up, grey jogging bottoms and a brown scarf over face.
He walked with a limp.
Anyone with information can call Northamptonshire Police on 101 or Crimestoppers, in confidence, on 0800 555111.