The night watch / Neil Lancaster.

He'll watch you. A lawyer is found dead at sunrise on a lonely clifftop at Dunnet Head on the northernmost tip of Scotland. It was supposed to be his honeymoon, but now his wife will never see him again. He'll hunt you. The case is linked to several mysterious deaths, including the murder of the lawyer's last client -- Scotland's most notorious criminal -- who had just walked free. DS Max Craigie knows this can only mean one thing: they have a vigilante serial killer on their hands. He'll leave you to die. But this time the killer isn't on the run; he's on the investigation team. And the rules are different when the murderer is this close to home. He knows their weaknesses, knows how to stay hidden, and he thinks he's above the law...