The Third Form at St Clare's recap

The third form undertakes its own end-of-term play while new pupils Rachel Denman, Libby Francis, and Fern alter the form's friendships. Rachel's talent for writing and directing survives the exposure of her failure as an actress. Fern, jealous of Rachel and of Carlotta's closeness to the Francis family, engineers several acts of sabotage and eventually cuts the play costumes. Carlotta is seriously injured while rescuing Fern from a runaway horse, but recovers. Fern confesses and leaves St Clare's, later sending an apology. Janet admits that jealousy drove her hostility toward Carlotta, and they reconcile. The form overcomes damaged scenery, illness, injury, and ruined costumes to stage Rachel's play successfully. Rachel departs for specialist theatre training, Libby leaves for America, and Janet is named the next head girl while Carlotta remains at school and expects to continue riding with Will.

Previously at St Clare's, Carlotta, Janet, Alison, Pat, Isabel, Bobby, Hilary, Gladys, Mirabel, and Doris have become established members of the same form. Their friendships and responsibilities shape the group before the new term begins. Pat and Isabel are twins, while Janet and Bobby are close friends. Bobby's enthusiasm for practical jokes is already familiar to the others. Hilary has served as form head and is known as a responsible pupil. Carlotta's earlier life in a circus has given her exceptional skill and confidence with horses, an ability that distinguishes her among her schoolmates. The rest of the form includes Alison, Gladys, Mirabel, and Doris, who return with the others as the pupils move into the third form. Miss Theobald continues as headmistress of St Clare's, overseeing school life and the pupils' conduct. Mam'zelle remains their French teacher. These existing relationships, Carlotta's riding background, Hilary's experience of leadership, and Bobby's taste for mischief provide the shared history carried into the new term.

At the start of term, the pupils learn that the nearby Oaks is now a riding stable. Libby Francis and her cousin Fern join the third form as day girls, giving Carlotta a welcome chance to ride. Carlotta impresses Libby's brother Will by handling the difficult Rocky and becomes friendly with the Francis family, which arouses Fern's jealousy. A second newcomer, Rachel Denman, speaks proudly of her actor parents and her own theatrical ambitions. Her manner isolates her from most of the form, although Alison befriends her and becomes caught between Rachel and Fern. Carlotta is selected as form head ahead of Janet and then narrowly defeats her in the vote to direct the form's end-of-term play. Janet tries to hide her disappointment, but tension grows between them. The pupils invite anonymous scripts, and Carlotta and Miss Adams select Lady Dorinda's Diamonds. Rachel is revealed as its author, and the script's quality improves her standing. Carlotta asks Rachel and Janet to help with auditions. Meanwhile, Bobby and Janet prepare a classroom haunting for Mam'zelle, and Fern begins seeking information about Rachel's past at De Winter Academy.

Bobby, Janet, Pat, and Isabel stage their classroom haunting, but Miss Theobald detects the trick. Mam'zelle takes it in good part while assigning translation as punishment. Fern then sets back the stable clock, making Carlotta and Libby late for auditions and casting doubt on Carlotta's reliability. Janet and Rachel complete the casting, with Gladys as Lady Dorinda, Mirabel as her husband, and Doris as the comic policeman. The form also plans a midnight feast for Pat and Isabel's birthday. Carlotta reluctantly accepts responsibility for including the day girls, while her conflict with Janet remains unresolved. Fern brings Sara Jameson, a former schoolmate of Rachel, to St Clare's and learns the secret Rachel fears. During a rehearsal, Fern deliberately provokes Rachel and publicly reveals that De Winter Academy rejected her as an actress. The form condemns Fern, and Alison firmly chooses Rachel's friendship. Janet helps Rachel recognise that her real strengths are playwriting and direction. Carlotta is hurt when Janet proposes handing over the production during her absence, but ultimately agrees that Rachel should direct while she continues as form head. The decision gives Rachel a credible future in theatre, even as Janet and Carlotta's quarrel becomes open.

Fern offers Rachel an apology and behaves helpfully, but privately plans to use the birthday feast against Carlotta. When influenza confines Carlotta to the sickbay, Fern stays home and anonymously reports the gathering. Will overhears her call, rides to St Clare's, and gets Libby away before Mam'zelle catches the boarders. Miss Theobald restricts the participants to the school grounds for two weeks. Libby exposes Fern's betrayal to the form, and Carlotta leads the girls in excluding Fern until she shows genuine remorse. Rachel turns the restriction into extra rehearsal time, but the play meets several new threats: Doris develops a throat infection, rain destroys the scenery, and Mirabel injures her ankle. Fern then steals Carlotta's embroidery scissors, cuts the costumes, and leaves the scissors as false evidence. Before the discovery can be resolved, Fern mounts Rocky despite having no riding experience. The horse bolts. Carlotta catches him and gets Fern safely down, but Rocky rears as help approaches and strikes Carlotta on the head. Carlotta is left unconscious and taken for medical care. At school, the damaged costumes and planted scissors create suspicion, though the form refuses to treat the scissors alone as proof against Carlotta.

Carlotta remains unconscious for a time, but the hospital soon reports that she has revived and should recover. Libby tells Miss Theobald about Fern's conduct, while Janet recognises that her own jealousy has driven her coldness toward Carlotta. Fern confesses to cutting the costumes and leaves St Clare's to join her parents. The form saves the play: Miss Walker's classes replace the ruined scenery, Miss Stratton arranges costume repairs, and Alison suggests a wheelchair adaptation that lets the injured Mirabel keep her role. Janet visits Carlotta, admits her jealousy, and accepts Carlotta's acknowledgment that riding and her friendship with Libby distracted her from form duties. They reconcile. Carlotta returns for the production, which succeeds, with strong performances from Gladys, Doris, and Mirabel and particular recognition for Rachel's direction. Rachel announces that she will leave for specialist training in writing, directing, and technical theatre, while remaining Alison's friend. On the final morning, Libby says goodbye before leaving for America. Fern sends Carlotta a written apology, though lasting reform is not yet established. Janet's appointment as the next head girl becomes public, and Carlotta plans to continue riding with Will after the holidays.

Carlotta recovers from her head injury and returns in time for the play, which succeeds despite the earlier damage to its scenery and costumes, Doris's throat infection, and Mirabel's injured ankle. Rachel receives recognition for her writing and direction, then leaves St Clare's for training in those areas and technical theatre. Her friendship with Alison continues. Fern confesses to cutting the costumes and is withdrawn from the school to join her returning parents. Her written apology admits the harm caused by her jealousy, but whether she will truly change remains unsettled. Janet and Carlotta acknowledge the jealousy and neglect that strained their friendship, reconcile, and look toward a new start. Carlotta remains form head for the close of term, while Janet is to become head girl next term. Libby leaves for America to work with horses. Will and Rocky remain, and Carlotta plans to ride with Will again. The feast punishment and the production crisis are both concluded as the pupils leave for the holidays.