Diablo appears when Lisa is out on a ride with Prancer, and she quickly gallops after him. Lisa returns to Pine Hollow excited about Diablo's return, but Stevie and Carole are skeptical and try to resume their study session for exams just days away. Unfortunately Lisa is more distracted than ever and she promises to study only after they find him. Lisa leads Stevie and Carole to the forest trail, but their search turns up nothing. Lisa tells Stevie and Carole that she'll continue looking for him alone. Diablo finally returns to Lisa and she brings him back to Pine Hollow. Later that day, Stevie is concerned when Belle falls ill and the vet suspects a virus. When the vet asks if Belle has been exposed to any wild animals, it finally dawns on Stevie - Belle was in contact with Diablo. Lisa leads Mrs. Reg, the vet, Carole and Stevie down to Diablo only to find the paddock empty. As Belle's condition worsens, Stevie blames Lisa for bringing a diseased animal to Pine Hollow and Lisa realizes if Belle is sick then Diablo might be too. Carole manages to convince Lisa to take her exam before she goes to find Diablo, but Lisa can't concentrate during the test and runs out upset, determined to find him. Lisa returns after searching for Diablo to find Stevie watching over Belle, her condition hasn't improved. Meanwhile Mrs. Reg insists that Veronica help a very shy girl, Lilly, prepare for her practical exam. Veronica takes over coaching from Simon and Desi, and surprisingly her loud and abrasive methods have unexpected results. And Trouble thinks that Melanie and Jess are too focused on their study to pay him attention, so he forces them to notice.