The Demon's Lexicon Trilogy

Sixteen-year-old Nick and his older brother, Alan, are always ready to run from the deadly magicians who use demons to work their magic. The magicians want a charm that Nick’s mother stole—and they want it badly enough to kill. Alan is Nick’s partner in demon slaying and was the only person he trusted in the world…until Nick begins to suspect that everything Alan has ever told him is a complete lie.