Caleb discovers that fellow rebels have been turned into zombified Trance Marchers by the sound of a magical object called the Horn of Hypnos. Thanks to the Horn, Phobos and Cedric now use the rebels as a workforce. Blunk steals the Horn and brings it back to Earth, and the trance spreads to Heatherfield. The Guardians are called in to help save the Horn's victims on School Dance night. Only a specific melody can break the spell, but how long will Will, Irma, Taranee, Cornelia and Hay Lin be able to resist the entrancing sound of the Horn of Hypnos? Hay Lin gets turned into a Trance Marcher. The only way they can get her to stop slamming them into a wall is to pull the plug on her power. In the B-story, Will is happy when she finds out that she will go to School Dance night with Matt.