One October morning, high school junior Bryan Dennison wakes up a different person-helpful, generous, and chivalrous-a person whose new admirable qualities he doesn't recognize. Stranger still is the urge to tie a red sheet around his neck like a cape.

Bryan soon realizes this compulsion to wear a red cape is accompanied by more unusual behavior. He can't hold back from retrieving kittens from tall trees, helping little old ladies cross busy streets, and defending innocence anywhere he finds it.

Shockingly, at school, he realizes he used to be a bully. He's attracted to the former...