During her orientation week at university, Ursula mistakes Lysander for an ex-boyfriend who dumped her a year earlier.
The pair strike up a relationship and move in together, but Lysander is convinced that she is still in love with her ex-, Eduardo.
During tests for a cerebral aneurysm, it is discovered that he has certain anatomical brain abnormalities that might be indicative of sociopathy.
Meanwhile, Ursula wins a lucrative scholarship to the Australian National University, but it means relocating to Canberra. Lysander quits his job as a car salesman, decides to write ‘the Great Australian Novel’ and secures a part-time job as a ‘filler’ on police lineups.
What ensues is a psychological thriller that follows Lysander’s attempt to commit the perfect murder.