The book begins with converted Viking Njall and his associate Etain as they seek refuge in a cave, which turns out to be inhabited by Grimnir the last of the skraelingr. Grimnir is an interesting character as he's an ogre, formor, troll, or whatever you want to call him but he is also the last real remnant of the culture which once destroyed his kind. He serves as the entirely unsympathetic view of Christianity and Norse culture both. He is an excellent creation for those who like dark antiheroes like the Hound of George R.R.Martin's A Song of Ice and Fire, the Black Thorn from the Ties That Bind, or the Black Dow from the First Law Trilogy.
Part of what makes grimdark unique from other fantasy exemplars, at least when it's actually supposed to grimdark versus something passed off as it (yes, the No True Scotsman fallacy) is presenting characters who embody moral ambiguity as the protagonists. Grimnir is an awful person, if you can call him a person at all, and a monster who gets a lot of people killed both likable and otherwise.
There's no attempt to soften him by putting him up against worse creatures or showing a hidden soft side--beneath his monstrous orc-like exterior is a monstrous orc-like interior. Yet, there's an honesty about what he is which becomes refreshing against many of the hypocritical characters around him. I both hated and understood Grimnir, which made him an interesting character to follow on his mission of murderous vengeance. I respect Scott Oden for not going the easy way and turning him into a big cuddly teddy bear but remembering we're following a monster throughout. This is a story of Norse mythology and Christian conquest as told through the eyes of Grendel rather than Beowulf.
Etain is a character which also serves as an excellent foil for Grimnir. A pacifist but well educated Christian in a land defined by blood and vengeance, you have to wonder how well their faith will hold up while traveling with living embodiment of mythology. I found their struggle painful and believable, especially as their situation kept going from bad to worse. Those who expect Scott Oden to come down on one side or another in the war of the faiths will be pleased to know they actually did a great job making an exemplar of Christian virtues--it's just, well, almost no one else seems to follow them on Etain's side.
The book is divided into multiple "books" which work as a series of novellas that reflect Grimnir and Etain's adventures. This is a common fantasy trope and feels a bit like a Dungeons and Dragon's campaign except all of the conflicts are bloody as well as horrifying. We get to see exactly how both the "heathen" and Christian forces treat one another as well as the hypocrisies on both sides. For one potentially triggering example, poor Etain witnesses a group of Christian warriors who are about to rape a female prisoner but only back off when they find out she's one of their faith--which gets their leader to try to figure out a way she doesn't qualify as a "real" Christian. Another moment has a Celtic god hesitate to destroy a city full of innocents with an earthquake until Grimnir points out they're all Christians so they don't count. No one comes out looking good during this battle between religions because everyone, at the end of the day, is human.
Even the nonhumans.
The novel is a bit slow getting started but becomes one of the better ones I've read this year by the end of the first few chapters. It is a dark hard-R rated fantasy which pulls no punches and never really let's up from beginning to end. None of the violence is gratituous but reflects this is an evil world and that is why I strongly recommend this book to those who enjoy pitch black storytelling. Few people can write as intelligently about stupid self-serving evil warping good enlightened ideals--be they pagan honor or Christian peace. A must have for those who enjoy mythological historical fantasy.