A 31-year-old woman on a night out in Peterborough fought off an attack after accepting a lift from a man she believed to be a taxi driver.
She had been drinking with friends before trying to get home at about 0400 GMT on Christmas Day.
A dark grey car, possibly a Vauxhall Vectra, stopped as she walked along Park Road, police said.
The driver took her to Uldale Way in Gunthorpe and returned a short while later and tried to force his way in.
She managed to fight him off and he fled, police said.
The offender is described as 6ft (1.8m) of medium build, with short blond hair.
Det Sgt Adam Fraser said: "This was a terrifying incident for the victim who showed great bravery to fight off the attacker.
"I would appeal to anyone who saw the vehicle in Park Road or the man running off along Uldale Way following the attack.
"The offender may have sustained facial injuries during the incident and I would like to speak to anyone who has a friend or relative with unexplained marks on their face from around that time.
"I would also urge people to ensure they use licensed taxi companies and book in advance where possible."