Amy floats, so off she is sent to Drearcliff Grange School in the 1920s, a dour and forbidding place ruled by fear, but also home to an odd selection of girls, some of whom, like Amy, are a bit Unusual. When a cell-mate vanishes Amy forms the Moth Club to find her and bring her home, but that adventure is merely a prelude to a dark and terrible force that begins to control Drearcliff, and which replaces an arbitrary system of rules and punishments with an inhuman conformity designed to summon cosmic horrors. Only Amy and a few remaining outcasts stand against world domination!

Expanding on a previous story, this is boarding school fiction turned up to eleven, crossing Xavier's School For Mutants with pulp heroes and villains from the early 20th century with Enid Blyton meets Lovecraft. It's all fantastic fun, witty pastiche but wonderful characters and cutting points about power and growing up and the limits of responsibility. Jolly good show.