The O'Sullivan twins are thrilled to be returning to St. Clare's as proud members of the second form! No longer the youngest girls in the school, Pat and Isabel are eager to enjoy their new privileges, fiercely competitive lacrosse matches, and, of course, their legendary midnight feasts. But they quickly discover that being in the second form brings its own set of unexpected challenges.

With two strict new form captains, Mirabel and Gladys, demanding absolute loyalty and hard work, the girls are pushed to their limits on the sports field and in the classroom. The real trouble, however, begins with the arrival of a deeply spiteful and sneaky new girl, Elsie Fanshawe. Elsie loves nothing more than eavesdropping, spreading nasty rumors, and getting the other girls into terrible trouble with the mistresses. When Elsie's scheming threatens to completely ruin the term and tear their friendships apart, Pat, Isabel, and the rest of the second form must band together in a thrilling showdown to teach the school sneak a lesson she will never forget!