If I'm honest I didn't think this would be my sort of thing. Happily I was pleasantly surprised & I really enjoyed it. Even though the story follows a pair of teenage twins (one reason I didn't think I would enjoy it), anyone of any age will enjoy reading it & there is pretty much something for everyone. I particularly liked the historical facts, which were cleverly integrated as part of the story, learning without even realising it ;-) It is a fast paced story with plenty of action & adventure, in some parts you are on the edge of your seat watching & waiting for the outcome, hoping the twins will outsmart the bad guys, as you try & work out if ? is really on their side or not!
I told my son bits about the book as I was reading it, he's at that age where he only reads when made to at school. Imagine my surprise when he asked if he could read this sometime!
In a nutshell Zero is the Key is a cleverly written, fast paced book full of action, adventure & intrigue which I highly recommend to everyone.