M.I.A. and the Book of Damien by Shawnee Morris

Now reunited with his friends, Alex embraces the world of weird in front of him. But they can't go home just yet- the problems in the forest are much bigger than they seem. The creatures here need their help. So just one more thing before they go back to their normal lives, right? They'll steal something that will help the creatures in need ward away the threat that looms above them. All goes well until they have the stolen item in their grasp. They can't go home now. Not while they're tangled in this web of deceit.