After discovering that injured animals come to the barn in her backyard for help, it is up to Zoey and her cat Sassafras to help new arrival Marshmallow, a sick baby dragon.
When her first two attempts to help a monster with his embarassing problem go awry, Zoey and Sassafras will have to find a solution quick if Gorp is to make it to the annual monster ball.
Making a terrible discovery at the stream about a mysterious threat that is endangering its magical creatures, Zoey and Sassafras race against time to discover the source of the problem and save the Merhorse species.