Miss Kennedy temporarily teaches History at St. Clare's, substituting for her ill friend, Miss Lewis. Her sole reason for taking the post is earning wages to support her ailing mother's nursing care. Financially dependent on this income, she struggles profoundly with classroom discipline.

Her timid nature invites relentless student pranks. Exploiting her known fear of cats, students hide a cat named Sooty in her classroom. They also throw firecrackers into the classroom fire during lessons. The chaos causes her deep distress, prompting her to feign illness and retreat from class once. Privately, she confides in her friend Miss Roper, confessing feelings of inadequacy and thoughts of resigning due to her inability to control the students. During one such conversation in a town tea shop, she voices her anxieties about her mother's care and her precarious job, unaware that students Patricia O'Sullivan, Isabel O'Sullivan, and Kathleen Gregory eavesdrop nearby.

This overheard conversation sparks a crucial change. The students, confronted with the personal consequences of their actions—particularly how her resignation would threaten her mother's care—organize a collective apology. They write remorseful letters and pledge to stop targeting her with pranks.

Despite her hardships, she shows compassion towards the students. Discovering clear evidence of an unauthorized midnight feast, she deliberately ignores the disturbance, attributing suspicious noises to "mice" to shield the girls from punishment. This leniency, combined with her earlier vulnerability during the tea shop confession, gradually transforms the students' perception of her. Her tenure concludes at term's end when the recovered Miss Lewis resumes her teaching duties.