A schoolboy had a knife held to his throat during a robbery close to the bird aviary in Abington Park.
The offender approached the 14-year-old victim from behind before holding him in a headlock grip and producing a 12-inch kitchen knife which he held to the victim's throat.
The robber demanded the victim's phone and money before searching his jacket and trousers. He then ran off towards the roundabout on Park Avenue South.
He was 6ft 1in tall, skinny and aged in his 20s. He was wearing a full black tracksuit, black gloves which had a white Nike tick on the top of them and all black Nike Air Max trainers.
Anyone with information about the attack which happened between 8.40am and 8.50am on Wednesday, June 28, should call Northamptonshire Police on 101 or Crimestoppers, in confidence, on 0800 555111.