It is November 12, 1975. Australia has been thrown into political upheaval with the sacking the previous day of Gough Whitlam as Prime Minister. At Balmain Boys High School, teacher Susan Ross is plunged into her own state of turmoil following the murder of the school's science master - gassed in his own laboratory. Who killed him? The problem is there is no shortage of people who might have wanted him dead: the school's bad boy, the headmaster, the impeccable school captain, the rather vague English master - and that's just the beginning.