When I was much younger there was a series of books of world myths and legends that I devoured. This resonated quite well with me and the Norse myths and legends I read at the time. (It also gave me big clues about what was going to happen in the book and what's going to happen in the next books)
Dublin was a viking settlement, there's evidence all over the place of this, and this uses that fact and plays with it. Arthur Quinn has to move from Kerry to Dublin with his dad when his dad gets a job working for the metro north. He's been having strange dreams about ancient warriors and now they're getting more and more frequent. In his new school he makes new friends Will and Ash and finds himself embroiled in a war that might destroy the world.
It's interesting but there were moments when my suspension of disbelief was strained a little. Seriously those kids need to get themselves to a library and do some research. They also came across as a bit older than the about 12 they were supposed to be. As well there weren't enough descriptions of where people were to truly satisfy me. Though it did drag me in and I resented having to go back to work rather than continuing to read it.
I enjoyed the read and I expect that it will engender a lot of discussion, I have a pretty good idea what the hammer is, Ash is a great solid female character as well and the story has potential.
Now, I wonder how they'll deal with Fenrir.
