The Devil on the Road — Robert Westall

Caught in a freak storm, John Webster takes shelter in an old barn with weird symbols carved in the doors. The landowner offers him a place to stay and John, on leave from University, takes him up on the offer.

But it turns out the barn has more history than he first suspected. A portal back in time, to be precise. He meets the beautiful Johanna, who is being tracked by the Witch Finder General. Modern science says that witches aren't real... but then, neither are portals back in time, so what can John believe?

John finds himself torn between the past and the present, caught in a web of magic, mystery, suspicion and witchhunts.