- Thérèse and Laurent start leading separate lives of debauchery: Thérèse has affairs with other men, while Laurent begins to drink and consort with other women.
- They become increasingly suspicious of each other, each thinking that the other will inevitably confess to their murder.
- The two realize that this miserable state of affairs can't go on forever, and the same idea occurs to them at the same moment: Laurent decides to kill Thérèse because he's afraid she will destroy him, and Thérèse decides to kill Laurent for the same reasons.
- A match made in heaven, Thérèse and Laurent.
- The next day, Laurent steals a flask of poison (prussic acid, to be exact) from the laboratory of one of his chemist friends.
- And Thérèse sharpens a kitchen knife and hides it in the sideboard.
- Game on. (Murder 2.0, that is.)