Halloween Night Fever: Mirror Mirror on the Wall

This novel takes place a year after "The Cir-Cuss Comes to Town" and before "End of the Long Walk". A greedy horse rancher captures a black unicorn that belongs to a headless horseman. Pessimistic Kitt Sassacus is training her optimistic cousin, Jessey Sassacus to take her place, but the mission becomes deadly when a psychotic entity named Bloody Mary is invoked and holds a college Halloween party hostage.