From The Horse's Mouth

Sabrina must add a physical education class to her college schedule and chooses beginner's horseriding. Unfortunately for Sabrina, she is assigned to a cranky and lame horse called Mission Impossible. If Sabrina cannot successfully learn to ride Mission Impossible in the next two weeks, she will lose face in front of her snobby classmate Debra and, even worse, Mission Impossible will be sold to a run-down holiday horse company. Staying on a horse is hard and learning to ride overnight is a mission impossible so Sabrina uses her powers to become a more competent rider. However, when Sabrina enters a riding competition she cannot use an ability spell or ride a magically enhanced horse. Now Sabrina can only hope that together she and Mission Impossible can use their own skills and strengths to win.