While the country hosts an annual four nations amazons jumping competition, horses are mysteriously spooked. The latest victim,princess Sofia of Prussia, also receives notes threatening with lasting consequences unless the bows out. The colonel, after whom the base's forbidden pet, a foundling dog, is named, orders ROX to go undercover. Stableboy Xavier and vet Olivia suspect the stud farm owner's daughter, who competes for their own country. Rick and Rox work out the method, ice darts. But the saboteur stops at nothing.
