A 76-year-old woman was assaulted at a house in Dunblane in the early hours, police have said.
The incident happened at about 0400 BST in the town's Springfield Terrace.
The woman, who has not been named by police, was taken to Stirling Royal Infirmary, where she was receiving treatment.
The area around the terraced house was cordoned off by officers. Police have appealed for anyone with information to contact them.
Det Insp Ronnie Isles, who is leading the investigation, said: "We have a team of dedicated officers currently carrying out inquiries.
"This type of incident is extremely rare and we appeal for anyone who may have been in this area around 3.30am to 4am. They may have been coming from or going to work.
"The inquiry is at a very early stage and we are unable to give out any further details at present."