During a particularly intense Florida heatwave, inept lawyer Ned Racine begins an affair with Matty, the wife of wealthy businessman, Edmund Walker. One night Ned arrives at the Walker mansion and playfully propositions a woman who he mistakenly thinks is Matty. The woman is Mary Ann Simpson, Matty's visiting high school friend. Soon after, Matty tells Ned she wants to divorce Edmund, but their prenuptial agreement would leave her with little money. Eventually Ned suggests murdering Edmund so Matty can inherit his wealth. He consults a shady former client, Teddy Lewis, an expert on incendiary devices, who supplies Ned with a bomb, though he strongly encourages Ned to abandon whatever he is scheming.