Frank the ogre has come to Monster Hospital with a tummy ache because he ate two nasty children for breakfast. Sylvie, Dylan, Carolyn and Tom - the naughtiest children in the school - are recruited by the mysterious Sister Winifred to be his doctors. The four not-exactly friends have to find out what's wrong with Frank without getting gobbled up or suffocating from the stupendous stink. After a trip in Frank's seven-mile boots and a confrontation with Frank's very grumpy mummy, they learn that their patient might not have been telling the whole truth about his tummy ache.