The Leap — Jonathan Stroud

After her best friend, Max, drowns, Charlie Fletcher is overwhelmed with shock and grief. When she attempts to explain what happened that day at the Mill Pond, no one believes her. The doctors and her mother think she may be hallucinating, or worse-crazy. Even her sympathetic brother can't understand what is happening to her. Charlie nearly died trying to save Max and as an aftermath to this terrifying experience, Charlie begins to have incredibly vivid dreams, where she sees Max walking far in the distance in a strange land. She tries to catch up, but she can never reach him. Sleep soon becomes her only passion. But one night, after waking up from a dream with cuts and bruises, she realizes that her nighttime excursions are real. She alone has the power to hunt for Max. And she knows he's out there somewhere. To save him, she'll follow his trail wherever it goes-even beyond the limits of this world.