Zack’s moods are like a rollercoaster. When Zack is on the down-swing, he feels extremely glum. When Zack is on the up-swing, he is extremely happy, giddily, and fun to be around. Zack’s parents notice that Zack’s moods are like a rollercoaster for no reason, so they take Zack to see the doctor. With the help of Zack’s doctor and counsellor, Zack and his family learn new ways to manage the rollercoaster, and the rollercoaster eventually flattens out.