I enjoyed this. It's a great mesh of fantasy and reality. I can't comment on any accuracy of druidry aspects, but the way it was woven worked for me. There's a touch of time travel in this, but it doesn't get bogged down in the logistics. They think about what might happen, but there is no "butterfly effect" here, which I appreciated. I liked Cormac and Sean. I liked Michael and Aoibheann and even Finnbheara also. 
 And I don't feel like over-analyzing, so I'm not going to.