Northamptonshire Police are seeking two men who called 999 to report an assault near a Wellingborough Road pub.
Control room staff received a call stating a man had attacked a woman close to the Fiddler's pub.
However, two men were on the line and one of them was particularly agitated, preventing police staff from taking details.
The only descriptions are that the man was white, with short hair and he had tattoos on his arms. The victim had blonde hair.
The attack happened between midnight and 1am on Saturday (October 29).
Anyone with information can contact Northamptonshire Police on 101. Alternatively, they can call the independent charity Crimestoppers, anonymously, on 0800 555 111.