The Demon's Covenant (The Demon's Lexicon Trilogy)

Mae Crawford’s always thought of herself as in control, but in the last few weeks her life has changed. Her younger brother, Jamie, suddenly has magical powers, and she’s even more unsettled when she realizes that Gerald, the new leader of the Obsidian Circle, is trying to persuade Jamie to join the magicians. Even worse… Jamie hasn’t told Mae a thing about any of it. Mae turns to brothers Nick and Alan to help her rescue Jamie, but they are in danger from Gerald themselves because he wants to steal Nick's powers. Will Mae be able to find a way to save everyone she cares about from the power-hungry magician's carefully laid trap?