Penny Simms is pony mad and is more than a little upset when a flock of foul-smelling pony vampires are found at the equestrian boarding school that she attends. They have been sent by the wicked Devlipeds to disrupt an official health and safety inspection, which the school must pass or risk being closed down. With the help of her intrepid friends, Penny does her best to rid the school of the unwelcome guests with hilarious and unexpected results.