The incident took place between 2am and 2.20am on Saturday (September 30) when the woman was walking along John Clarke Way.
She was attacked by a man who forced her to the ground and threatened her.
She screamed and fought him and he ran away.
The offender is described as white with a medium build, short messy dark hair and dark bushy eyebrows.
Anyone with information should contact Northamptonshire Police on 101 or charity Crimestoppers anonymously on 0800 555111.