3.5 Stars! What the heck--I'll give it a 4.
This is a fine YA novel for action-adventure-fantasy lovers everywhere. I am impressed that Mr. Marlowe is serious in his craft as he is improving with each novel. Well, I've only read one other, his first, but I intend, still, to commend Scott on his progress. (I hope he doesn't mind that I call him Scott--he is one of my GRFs, after all)
I'm not going to write a synopsis. The one at Goodreads is excellent enough. Instead, I'll concur that the characters are varied (an eslar mercenary, sorcerers, dwarves, hell hounds, demons, etc), interesting, well-drawn, and the action is nearly non-stop. In addition, a world is built reminiscent of Lord of the Rings and The Terminator, combined, with lots of precision and details.
Which brings me to the required mention of a nit: In more than one scene---I'd ignore it if it were only one scene---too many step-by-step descriptions were written without apparent purpose. Details such as a character putting one foot on the ground, then the other, etc etc can draw out tension, and I will read minutia with rapt attention for effect in a story, but for the life of me, I couldn't understand why I would care for a breakdown of every movement so often, for example, when a character was merely getting out of bed. In one case, the action should have been rapid-fire, but the read slowed due to step by step details that roll already in the average imagination. Of course, this is merely my average opinion and personal experience. Other opinions may vary.
In sum, good job, Scott. Thanks for the memories of a skinny white man and his hell hounds.