When their governess leaves to be married, seven lively sisters all arrive at boarding school for the first time: Pam, Gwen, Sylvie, Tony, Septima, Phyllida and Gerry. Queen Anne's School may never recover!

Following upon Seven Sisters at Queen Anne's, Septima at School is the second in a trilogy detailing the adventures of "the long family of Shortt"-seven sisters who attend the same school. But although Gwen and Sylvie appear briefly at the beginning, Pamela at the end, and Phyllida and Gerry intermittently, this is really the story of Septima and Tony, and the various mishaps they fall into during their second year at Queen Anne's. From getting her finger stuck in the spout of a tea-kettle during a "secret" picnic breakfast to convincing her sister that a burglar is intent on entering their dorm late one night, Septima is as much trouble as always, and Tony could be forgiven for exclaiming, at one point: "Life would be a lot simpler if it weren't for looking after you, Septima." It was the incident with the tea-kettle that led Tony to purloin a bell-handle, a worrisome circumstance that resulted in a number of exciting events involving Borzoi puppies, the kidnapping of a big brown mutt, and a surprising discovery after a most unusual entrance through the rotting roof of an old shed ...

Phyllida is one of seven sisters to attend Queen Anne's School, where they are known as the "long family of Shortt," responsible for a list of escapades to their credit and discredit. During the summer holiday, Phyllida tries to rescue a swan being hurt by a spoiled girl called Queenie, soon to be a student at Queen Anne's. The rescue mission ends badly, with Phyllida bitten by a dog and Queenie pushed into a river. However, the holidays conclude happily with the wedding of the eldest Shortt girl, Pam. Back at school, Phyllida likes beginnings so enjoys the first few days in the third form, and is delighted to see old friends and enemies. Naturally, the annoying Queenie turns up in her form, accompanied by a shabby and shy girl Violet. Phyllida's initial dislike of Queenie is renewed but her sympathy is awakened by Violet's discomfort. Will new girl Queenie ruin the term for Phyllida?