Under a watchful eye / Adam Nevill.

Under a Watchful Eye by Adam Nevill is a supernatural thriller from the award-winning writer of The Ritual and Last Days.Seb Logan is being watched. He just doesn't know by whom. When the sudden appearance of a dark figure shatters his idyllic coastal life, he soon realizes that the murky past he thought he'd left behind has far from forgotten him. What's more unsettling is the strange atmosphere that engulfs him at every sighting, plunging his mind into a terrifying paranoia. To be a victim without knowing the tormentor. To be despised without knowing the offence caused. To be seen by what nobody else can see. These are the thoughts which plague his every waking moment. Imprisoned by despair, Seb fears his stalker is not working alone, but rather is involved in a wider conspiracy that threatens everything he has worked for. For there are doors in this world that open into unknown places. Places used by the worst kind of people to achieve their own ends. And once his investigation leads him to stray across the line and into mortal danger, he risks becoming another fatality in a long line of victims . . . Google Books