Darrell’s final year starts with a fierce argument with Gwen, but she knows they need to work together. French student Celeste joins the Third and plays a prank on the teachers.

Alicia falls out with Darrell and the other sixth formers when she edits the school newsletter. Jo and Susan get into trouble with Mr Parker over his new typewriter.

The girls try to cheer up Celeste, who wants to get expelled so she can go home to see her mother. Mary-Lou finds herself facing a snail invasion when she takes an art class.

Irene offers to help Ron with his band, who are playing that afternoon, forgetting she has to take an important music exam. Felicity and June find clues to the missing time capsule.

Angry about not receiving a present from Paris, Celeste hides in the stables. However, she is trapped there with Matron when the stables catch fire.

Celeste lies that she started the fire on purpose to be sent home. Sally confronts Matron about her eyesight, and Miss Grayling finally tells Celeste the truth about her mother.

When Felicity and Darrell debate whether the Third should have the same freedoms as the Sixth, the sisters end up in a personal argument. Gwen’s attempt at matronly duties ends in chaos.

Matron arrives with Nancy, her young ward, and Gwen tells her to ask Matron to stay, which annoys Matron. Nancy joins the third formers as they search for the missing time capsule.

Jo causes chaos when she tells Celeste's mother that Celeste doesn't want to return home. Nancy, June and Felicity are excited to discover that Fred knows about the time capsule.

Alicia and Darrell are trapped in the cellar after Alicia receives some bad news. Can finding the time capsule help them? Irene feels pressured by her musical ambitions.