Detectives are appealing for witnesses after a man was sexually assaulted in Kingsthorpe Recreation Ground.
The incident happened about 50 metres away from the entrance close to the junction of Welford Road and Kingsway on Wednesday, August 29, between 9.30pm and 10.30pm, when a man was walking through the park.
He was approached by another man who pulled out a weapon, threatened him and then forced him to perform a sexual act, Northamptonshire Police today said.
A spokeswoman for the force said: "The offender is described as a white man, aged 30-40, of big build, wearing a beanie hat and a dark-coloured fleece.
"He spoke with a Polish/Russian accent."
Witnesses or anyone with information are urged to call police on 101. Alternatively, they can contact Crimestoppers anonymously on 0800 555111.