Maddie's return upends Split River High. As she adjusts, not everyone welcomes her back. Simon is trapped on the other side while the ghosts search for answers and dark new secrets about the school emerge.

New mysteries at Split River High force Maddie, Simon and the ghosts to choose between leaving the past alone or exploring it and triggering unseen dangers. Nicole joins a new circle, and Simon and Wally take a risky leap for answers.