The Hadrian's Wall Trail, just outside Chollerford - Northumberland, England

Someone was following her.

Sloane felt it like a tickle on the back of her head, like a shiver at the base of her spine. It had been with her for some time now - that creeping sensation of someone watching her, that dancing little awareness of some other presence, always just beyond her sight.

You're paranoid, she told herself as she trekked across a muddy pasture, her shoes ...