The Twins at St Clare's recap

Identical twins Pat and Isabel O'Sullivan arrive at St Clare's determined to dislike it after leaving Redroofs, but their defiance gradually gives way to responsibility and friendship. They accept school customs, improve their French, share punishment with their form, defend the remorseful Kathleen after her thefts are discovered, and help end the mistreatment of Miss Kennedy. A forbidden circus visit, reconciliation with the insecure Sheila, the rescue of a wounded terrier later named Binks, examinations, and the end-of-term concert deepen their place in the school community. Pat tops the geography examination, Sheila succeeds in a major concert role, and Binks is permitted to spend the holidays with Kathleen while her aunt considers keeping him. Miss Kennedy leaves because Miss Lewis is returning. By the final day, the twins openly love St Clare's and intend to return.

Pat and Isabel O'Sullivan leave Redroofs unwillingly when their parents send them to St Clare's instead of allowing them to follow friends to Ringmere School. Proud of their former status, the identical twins intend to resist the new school. They soon learn that their academic preparation is weak, especially in French, and that junior pupils are expected to perform practical tasks for seniors. Pat initially refuses to help Belinda Towers and uses the twins' resemblance to evade a restriction, but confesses after the deception affects lacrosse selection. Belinda forgives her and keeps her on the team. The twins later disobey Mam'zelle by attending the cinema before rewriting poor French work. Miss Theobald responds by arranging daily help rather than treating them as hopeless. Meanwhile, the first form repeatedly disrupts Miss Kennedy's history lessons. Janet Robins sets off firecracks in the classroom fire, creating a dangerous disturbance. When Janet confesses, the entire form, including the twins, voluntarily shares responsibility. Their apology keeps Miss Kennedy from resigning, and the twins gain their classmates' respect by accepting the punishment with everyone else.

Pat and Isabel have begun to move from deliberate opposition toward membership in the first form. After the firecrack incident, the whole form accepts punishment and apologises to Miss Kennedy. A secret midnight feast follows, and Miss Kennedy quietly gives the girls time to hide the evidence instead of reporting them. At the same time, money disappears from several pupils. Kathleen Gregory, formerly anxious and lonely, begins spending freely on a costly birthday gift and food for the feast. She also becomes more confident and earns a place with Isabel in an important lacrosse match, which St Clare's narrowly wins through their play. The theft problem becomes urgent when Janet loses five pounds. Rita George then catches Kathleen at her purse. Kathleen admits taking the missing money because she wanted to buy gifts and secure friendship, not because she sought things for herself. Pat and Isabel appeal to Miss Theobald on her behalf. Miss Theobald keeps the matter private, requires repayment, and plans to ask Kathleen's aunt to provide suitable pocket money. Kathleen remains at school with the twins' renewed trust.

The twins are academically caught up and accepted at St Clare's. After overhearing that Miss Kennedy needs her temporary salary while caring for her ill mother, Pat, Isabel, and Kathleen help bring about a joint apology from the first and second forms. The tricks stop, and Miss Kennedy becomes an effective teacher. A new conflict begins when a lacrosse ball breaks the first-form window and no culprit comes forward. Miss Roberts cancels the form's circus outing to pay for the damage, so Pat, Isabel, Kathleen, and Janet secretly cycle to the performance. Hilary later lets them back into the locked school. Queenie Hobart eventually admits that she broke the window but had been too ill to confess, clearing the form and earning it a replacement outing. The four truants decide they should not benefit twice, then develop colds from their night outside and miss the treat anyway. Their offence remains hidden. During half-term the twins admit that they are happy at St Clare's. When Janet humiliates Sheila Naylor for her boastful pretence, Winifred explains that Sheila is insecure about her family's recently acquired wealth and background. The twins and Janet offer practical kindness, and Sheila begins to abandon her superior manner.

Sheila first proves useful as prompter for the end-of-term play, then takes over Vera's major role after Vera breaks her arm and goes home. Pat, Isabel, and Kathleen find a wounded young terrier and secretly nurse it in an attic room, with Belinda choosing not to expose them. The recovering dog escapes into the school, and Miss Theobald conditionally allows Kathleen to keep it in the stables and take it home if her aunt agrees. Kathleen names it Binks. During examinations, Isabel accidentally sees what she believes are upcoming geography questions. She refuses to profit from them, and the paper turns out to belong to the second form. Isabel places sixth fairly, while Pat earns the top geography mark. The term concert succeeds: Sheila is acclaimed in Vera's former role, the French play goes well, and Doris Elward completes her solo dance despite Binks escaping and tripping her at the end. On the last day, Miss Kennedy leaves because Miss Lewis is returning, and the pupils thank her warmly. Binks goes with Kathleen for the holidays while her aunt decides his permanent future. Pat and Isabel acknowledge that they now love St Clare's, leave as accepted members of the first form, and intend to return willingly.

The winter term closes with Pat and Isabel fully accepted by the first form and no longer resisting St Clare's. Their work has improved, Pat has led the geography examination, and both sisters leave confident in their friendships and eager for the next term. Sheila's successful concert performance confirms her new confidence and place in the form, while Vera remains at home recovering from her broken arm. Miss Kennedy receives a warm farewell and leaves only because Miss Lewis will resume the history post. Kathleen takes Binks with her for the holidays, but whether the dog can live with her permanently still depends on her aunt's approval. The concealed circus outing is never reported, though the four truants already lost the replacement treat through illness. The school community's major conflicts are settled, with Binks's permanent home the principal open question.