A man indecently exposed himself and performed a sex act in front of a teenage girl in Desborough.
The incident took place shortly before 9pm last night (Sunday) in Roman Way.
The offender, who was driving a dark (possibly black) car, indecently exposed himself to the 15-year-old victim.
He then drove off towards the nearby Co-op.
The offender is described as bald, wearing glasses and aged 40 to 50.
He had a local accent and was wearing a white T-shirt.
Police are appealing for witnesses to the incident or anyone with information to contact them.
Witnesses should contact police on 101 or Crimestoppers anonymously on 0800 555111.