Two men wearing balaclavas broke into a house in Willoughby Road at about 6.45pm on Tuesday, March 10 and stole a substantial amount of money.
Once inside the property, the men forced the woman living there hand over a substantial amount of cash.
They then fled, leaving the woman in the property.
Detective Inspector Philip Mills, who is leading the investigation, said: “Incidents like this are fortunately very rare, but this was a nasty robbery which has obviously left the victim very shaken.
“I would urge anyone who knows anything about this incident to contact us as soon as possible.”
The two men are believed to be aged between 20 and 40 and may have been eastern European.
One was between 5ft 6in and 5ft 7in while the other was between 5ft 9in and 5ft 10in.
Witnesses, or anyone with any information about this incident, can call Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111 or use the anonymous online form at www.crimestoppers-uk.org.