Police want to speak to a member of the public who intervened after a 17-year-old girl was assaulted by three males.
A police spokesman said the girl was followed along Senwick Road, Wellingborough, by three males sometime between 4.15pm and 5pm on Monday. When she reached the junction with Midland Road, they assaulted her.
Detectives would like to speak with a member of the public who intervened, causing the offenders to make off.
Witnesses can contact police on 101 or Crimestoppers anonymously on 0800 555111.