The Dark Between the Trees by Fiona Barnett

1643: A small group of Parliamentarian soldiers are ambushed in an isolated part of Northern England. Their only hope for survival is to flee into the nearby Moresby Wood... unwise though that may seem. For Moresby Wood is known to be an unnatural place, the realm of witchcraft and shadows, where the devil is said to go walking by moonlight...
Seventeen men enter the wood. Only two are ever seen again, and the stories they tell of what happened make no sense. Stories of shifting landscapes, of trees that appear and disappear at will... and of something else. Something dark. Something hungry.
Today , five women are headed into Moresby Wood to discover, once and for all, what happened to that unfortunate group of soldiers. Led by Dr Alice Christopher, an historian who has devoted her entire academic career to uncovering the secrets of Moresby Wood. Armed with metal detectors, GPS units, mobile phones and the most recent map of the area (which is nearly 50 years old), Dr Christopher's group enters the wood ready for anything.
Or so they think.