Pig Island by Mo Hayder

Joe Oakes and Malachi Dove have known each other for years but the relationship was never a pleasant one.  Joe is a journalist and he investigated Malachi and his cult in its early days.  Malachi got into Joe's head and he barely escaped with his sanity.  But Joe's article made the American Southwest too uncomfortable for Dove, and he and his followers disappeared.

Now Joe has a lead on Dove.  It's rumored that he is the person behind the secretive cult on Pig Island off the western coast of Scotland.  Not that people have seen him.  No one sees the people on the island.  There is just one supply boat that comes to the mainland occasionally.  But people are getting curious and very uneasy. There are rumors of Satanic rituals.  A video has been leaked that shows a humanoid figure with a tail lurching through the undergrowth.  Joe's editor wants someone to find out what is going on, and Joe sees a chance for a book and to settle his score once and for all with Malachi.

Joe is given permission to visit the island.  Once there, he finds a small group of people, no more than thirty or so and deep divisions between them.  No one wants to talk about Malachi and no one wants to hear about the figure in the video.  In fact, it's pretty obvious that no one wants Joe there at all.  Before he leaves, he sets loose an evil that destroys everything in its path.  Joe barely escapes, taking Dove's daughter, who has never seen civilization, with him.  But the evil follows Joe, as it is rumored that Malachi also escaped.  Who will win the ultimate showdown between the two men?

Hayder is one of the finest crime/suspense novelists currently working. Her series about Detective Inspector Jack Caffery is regarded as one of the premier series available.   This is a stand-alone novel but it will give the reader uneasy nights and plenty of surprises along the way.  This book is recommended for mystery readers.