A man was punched in the face and threatened with a knife before being robbed of his mobile phone and cash.
The attack took place at about 3am on Saturday, August 25, when the victim, who was walking along Cannon Street close to the junction with Thomas Street, was approached from behind and punched.
He was then forced to hand over his mobile phone and cash.
The offender spoke with an African accent.
Anyone with information about the robbery can contact Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.