Hekla's Children is a novel that taps into horror, mythology, fantasy, archeology, and the British countryside. The monster of the story is the afaugh, sort of a British Wendigo: a spirit of cannibalism and greed which possesses people and makes them do terrible things. At the start of the novel, an ancient tribe plagued by the afaugh decides to make a sacrifice to hold it at bay.
Fast forward to ten years ago, when a group of kids on a scouting exercise in a small woodland adjacent to a city suddenly disappear when their group leader leaves them on their own.
Fast forward to now, when a skeleton is found in those very same woods, and an archeologist is called in to determine if it's old or young enough to potentially be a victim of a crime that the police need to solve...
Hekla's Children is in an outstanding novel. It mixes science (archeology), myth, the uncanny, horror, and a timeless mythological realm with great skill and fluidity. The closest comparison I can think of is The Truth Is A Cave In The Black Mountains by Neil Gaiman, which has a similar atmosphere, perhaps a little more condensed and distilled and sharp, but similar enough for this novel to belong in the same space as that novella.
It's not just a novel of atmosphere: the story never gets boring, and there is real tension at pretty much every stage of the book. I don't know whether the book is a "horror" novel, but it's dark and pretty ruthless in the way it treats its characters, and there is some fundamental dread at times when they are being pursued by the monstrous...
I can't think of anything to fault the novel for. It's entertaining, atmospheric and beautifully grim. Highly recommended to those who like their fiction dark.