The White Lady of Bicester House
The area around Bicester House is said to be haunted by a civil war ghost, still hunting for her hidden treasure.
According to the story, the unfortunate woman in question was left in charge of Bicester House while the house's usual occupants were off fighting for the King during the Civil War.
When the Parliamentary forces closed in on Bicester, the quick-thinking woman gathered up all the valuables she could carry from the house and threw them into a nearby pool known as Rookery Pond.
She presumably hoped that the Parliamentary men would search the house, leave empty-handed and she would be able to reclaim her valuables when the coast was clear. Sadly, the Parliamentary forces, frustrated at not finding the treasures that had hoped to plunder from the house, killed the woman.
The 'White Lady' is said to be seen walking the grounds of the house and the nearby streets on the anniversary of her murder, still searching for her hidden treasure. Even if she was still on the right side of the grave, the woman would struggle to find it as the pond has long since been filled in!
Notes on location
According to Historic England, only parts of the modern day Bicester House date back to the 17th century as the building was extensively renovated c1780 and again in 1820, so it is likely that the 'Bicester House' of the story refers to a different building on the same site.
I haven't been able to find the location of Rookery Pond, though there is a path known as 'Rookery Way' half a mile to the northwest which may hint at where this pond may have originally been.