I really enjoyed this exploration of what it is like to be in a cult, and I enjoyed the ambiguity about what it really going on. 

Narratively, I thought it was well done - we follow the voices of three characters, and a fourth narrative strand that comes from the Bastion as a group, or as a collective. Other parts of the story - the viewpoints from those on the outside - come from the media - social and otherwise. 

The characterisation of a social media pile on works well, and I love how the author follows that through to reflect the mob mentality that arises at the climax of the book, not dissimilar to the frenzy that the Bastion find themselves experiencing.

I like a book that leaves plenty of questions unanswered, when done well it certainly makes you think, and that is what this book has done for me.