Hettie discovers a map in the library which leads to a secret panel revealing a corridor leading to 'The Black Hole Club'. The Club has been dormant for 200 years and must be kept top secret. The "Black Hole Club" was a club started by first years 200 years ago, and Belladonna and Cynthia push their way in, to the dismay of Hettie, Mona and Cressie.
If the teachers find out the girls will be in trouble. Hettie, Cressie and Mona find 'The Book of Trivial Magic' and learn to magic never ending sweets, mad hair do's and all sorts of other trivial magic. Hettie becomes the leader of the club but is soon challenged to a leadership battle when Belladonna also discovers the club. Belladonna causes chaos with the Book of Trivial Magic and soon things become desperate. Hettie is thrown out of the club and soon Belladonna becomes out of control as leader. When Mona and Cressie are shrunk by Belladonna, Hettie has no alternative than to confess all to Miss Hardbroom.