After taking the new girls to Miss Grayling's study, the two agree that the only real failure in Darrell's year is Gwendoline.
To the other girls' disgust, she boasts about the cruel and unkind exchanges she had with her father to emotionally blackmail him into agreeing to her plans.
Amanda undertakes to coach June in tennis and swimming, predicting that she will be in the school second teams by the end of the term.
Gwen is sulky and obstinate, and finally maliciously tells Darrell that she is glad that she has made her father miserable: "It will teach him a lesson!"
Darrell, appalled, reports her failure to Miss Grayling, who predicts that a terrible punishment is in store for Gwen.
Jo decides to run away from the school, taking her friend, the weak and easily influenced first former Deirdre Parker.
Soon afterwards, Miss Grayling is told by the police that two of the stolen notes have been presented at local shops by two Malory Towers girls.
Amanda wants to swim in the open sea, but underestimates the strength of the currents and finds herself in danger of being dashed against the rocks.
In an emotional ending, Alicia takes June by the shoulders and asks her to carry on and hold the standard high.
“I said cruel things, I hurt him—oh, Miss Winter, why didn’t you stop me?” cried Gwen, her face white and her eyes tearless.
The Second Form is more prominent in this book, with Darrell and most of the other Sixth Formers having little to do beyond reacting to Gwen's latest display of selfishness.
New girl Suzanne, Mam'zelle Dupont's niece, is developed minimally as a character and serves mainly as a means for Blyton's recurring trope of a French character mispronouncing English words, reminiscent of the more successful Claudine in the earlier St. Clares series.
"In Jo's case, her father's part in her downfall is not in doubt, and they depart the school sadder and wiser people.
Letters from both Jo and Gwendoline after their departures are contrite and warmly written, giving the reader hope for their characters' futures.