The Tapestry #4: The Maelstrom by Henry H. Neff

My name is Max, and Rowan is bracing for war. Prusias is waging a war against the other demons, and he has a secret weapon to guarantee his armies will win. After his victory, he'll turn his forces and that weapon on Rowan. David and I discovered the secret has something to do with spider-like creatures that have been combined with technology. Rowan's experts are studying this problem, and I hope they'll figure it out before it's too late. I'm doing what I can to help by training a group of unwanted refugees called the Trench Rats, but I've got to watch my back too. I've been targeted for death by a group of relentless assassins whose stories of success are legendary. These executioners can take any form, even possessing my friends, so I can't trust anyone. 

You really need to read the other books in the series to fully understand what's going on. Demons in the last book prepared for war, and this book continued the hostilities. Prusias and Astaroth are the main antagonists, although Astaroth is waiting for his moment. The most intriguing parts of the series are the dynamics of Max's character. Max has been dealing with internal issues since the series began, and he continues to struggle with his own identity. There is Old Magic and power coursing through him, but there is also a chance he'll be overwhelmed by it. Most people in Rowan are awed by Max which makes it hard for him to develop close friendships. Luckily, he still has David, but another character becomes very important in Max's life. The series basically tells a story pitting good versus evil, but it also delves into humanity. Rowan is fighting for the survival of all humans on earth and all that goes along with it. The Demons see love, caring, and compassion as weaknesses. Max constantly deals with these emotions, but he always comes out on top in the end. I recommend you give the books a shot.