A woman is strangled in the bath by a black-gloved killer who disposes of her body in a large trunk. The trunk is delivered to St. Hilda College, an exclusive finishing school. Betty-Anne, one of the female students, is strangled in the school cellar. The police, led by Inspector Durand, are called in to investigate. Suspects include La Floret, the voyeuristic gardener; Di Brazzi, the new swimming instructor; Mrs. Clay, the summer school French mistress; an old professor who collects birds; and a philandering young teacher called Richard. The murders continue but Jill, a keen amateur detective, helps the police identify the unlikely killer..