Schism: Illirin Book One
Art therapy hasn't done squat for Gabe Jones. A thousand sketches of his fiancée can't bring his memory, or her, back to him. Nothing on Earth can. His past lies in another dimension, a world just out of sight.
Another student on campus, Lea Huckley, unknowingly shares Gabe's obsession with the fourth dimension. The monsters from the other side attacked her parents and fled, getting her folks locked up in the loony bin. Proving this other world exists is the only way to free them. Lea and Gabe strike a deal to help each other, and together they manage to open a door to the world of Gabe's true origin. She'd use him for proof - if she didn't already care too much.
While Gabe tries to reconcile his feelings for Lea and his rediscovered memories of his fiancée, a much more sinister plot unravels. He uncovers his history just in time to become the unwilling lynchpin in a conspiracy to start a war. His memory holds the secret to the final riddle the would-be conqueror needs to get the upper hand. Gabe must protect the riddle at all costs, even if that means leaving Earth, and Lea, behind forever.