Artemis wants to find out why demons are time-warping in random places. But in order to do that, he must capture a demon at one of it's sites. So Artemis must race against another 12-year-old criminal mastermind (that he happens to fall in love with), to capture the demon. Then he must help the demons preclude their land from being destroyed.
Once again, I loved this book! During the climax, I was on the edge of my chair the whole time. I loved how it relied on the antagonist to be forced to help the demons preform their ritual. I even fell off the edge of my chair! The other thing that surprised me is that Artemis falls in love! He wonders to himself if it's normal.