Thirty-three-year-old journalist, Jim Holden, is obsessed with the mysterious disappearance of former Australian prime minister, Harold Holt, who went for a swim near Portsea, Victoria on December 17, 1967, never to return. This obsession with Holt's disappearance helps Jim hide from depression, brought into being by the dissolution of his marriage, and an unfulfilled desire to write feature articles. On the thirty-sixth anniversary of Holt's last swim, Jim meets two alluring young women at a pool party, one of them claiming to be Harold Holt's mistress. As the night wears on, Jim finds himself in the backseat of a car, behind the two vintage sirens who have decided to take Jim to Portsea for a midnight swim ....