A 30-year-old woman was sexually assaulted in Abington Park in Northampton.
Officers are now appealing for witnesses to the incident which happened in the park on Wednesday evening.
A 30-year-old woman had been with a group of friends in the top part of the park, near Ardington Road and Wellingborough Road, between 6pm and 9pm on Wednesday July 30.
At some point in the evening the woman was left alone with one of the men who sexually assaulted her.
Police would like to speak to anyone who may have been in the bandstand area of Abington Park on Wednesday evening, and saw a group of men and women socialising.
One of the men in the group is believed to have been acting in an abusive and intimidating manner, causing other members of the public to leave the park.
The offender was a white man with fair hair, 5ft 6ins, of medium build and in his mid-20s. He had a tattoo on the left side of his neck and was wearing blue shorts with big white flowers on.
Witnesses, or anyone with information about this incident are asked to contact police on 101 or Crimestoppers anonymously on 0800 555 111.