A teenage Kettering robbery victim handed over a bike as he feared his attacker may have had a knife.
The 14-year-old boy was on his friend's bike at about 5pm on Grafton Street on July 22 when the incident took place.
A black man came up to him from behind and told him to give him the bike. The boy then gave it to him.
A police spokesman said: "He was scared that he may have had a knife."
The attacker was described as wearing black clothing and with a balaclava on.
The bike he stole was a green and black Carrera Hellcat mountain bike.
No arrests have yet been made but police are urging witnesses or anyone with information to contact them.
They can do so by calling 101 or Crimestoppers anonymously on 0800 555111.