Katherine Mary Gordon, age 14, is in the care of her Aunt Luce, a famous artist, while her parents are working as medical missionaries in China.
Her mother asks Aunt Luce to arrange for Katherine to be sent to boarding school to complete her education. Aunt Luce, remembering vaguely that a friend of the family teaches at a Chalet School, makes inquires and determines that there are three Chalet Schools. One of them is only a Prep (Preparatory) School. Aunt Luce enrolls Katherine in one of the other two schools, selecting from the different schools on the basis of the uniform colours.
Arriving at the school, Katherine finds that her name has been switched to Mary Katherine Gordon, and further finds that two trunks of clothing have arrived, only one of which she packed. Meanwhile, Aunt Luce has disappeared on one of her sketching trips and Katherine's parents are out of touch due to war in China.
Katherine is assigned to the Upper Fourth, where she quickly becomes friends with Hilary Wilson.
This being a summer term, Katherine finds the games to be great fun, and she in turn is perceived as a real asset as she is a fine swimmer and outstanding tennis player. She also finds that she is able to do well at lessons, particularly French, but does have some difficulty with Art - and Herr Laubach!!!
Then a letter arrives at the school, informing the school that Mary Katherine Gordon will not be attending school that term. At the same time, word reaches the school that Katherine's parents have been put into interment camps.