Alan and Nick have been on the run most of their lives. First, they moved around with their parents as magicians hunted for them. The magicians are determined to get back something their mother stole from their leader Black Arthur.
Now that their father is dead, the brothers struggle to survive and hide with their mom in England. Alan, the nice one, can't say no to anyone, so when Mae and Jamie show up at their doorstep needing help, the whole family is sucked in. Before Nick knows it, Alan has the mark of a demon and it's a race to survive and save his soul.
Most of this story is told from Nick's perspective. He has a dark side that he struggles with constantly, and the story is well-written and told from his side. Alan and Nick are fully developed and complicated, and there are twists and turns throughout the story to keep anyone interested. There are a few things that are left unexplained--hopefully the sequel, The Demon's Covenant, explains those.