A pensioner has been taken to hospital with head injuries after she was involved in a hit and run collision on Monday afternoon.
Paramedics were called to the 73-year-old female pedestrian outside the Swan pub in Olney High Street at 3pm.
Police are appealing for witnesses from anybody who was in the area.
The driver of the unidentified vehicle involved failed to stop, say officers.
Police would particularly like to trace the driver of a white lorry seen in the area at the time.
Anybody with information should contact PC Liz Johnson on 101 or call Crimestoppers charity anonymously on 0800 555 111.