"Folk horror at its finest! The sense of dread and violence gives way to something much more terrifying and supernatural!" Hazel Chapel has escaped to a remote Scottish island with her two boys having escaped an abusive relationship. The break will give them time to heal as well as climb the single mountain, commonly known as The Pig. They have been given the keys to an out of season activity centre but are soon joined by an unwanted gang of teenagers who have no business being there. With no immediate escape, Hazel tries to protect her children from the attentions of the gang but soon realises that things are far more terrifying than she first imagined. What is the real reason for their presence? Are the horrors she is experiencing actually happening or just a result of Hazel's deteriorating mental state? And what is actually living under the mountain?