With sales of over 6 million books worldwide, the Animal Ark franchise is a hit with young readers. It's exciting enough that Lisa and Paul Cooke, two American stunt riders, have moved their team of mustangs to Yorkshire, England, and asked that Mandy and James help out at their ranch. When Mandy's favorite band, the Cowboys, show up there to film a rock video, the two friends know they're about to have the spring break of their lives! But the day before the shoot, Cougar, the lead mustang, develops a life-threatening illness - worrying his owners and infuriating the video producer. Will Mandy be able to help the sick horse back to health, despite the odds against him?