Joan Didion's novel The Last Thing He Wanted is a political thriller with three main characters and four minor ones.

Elena McMahon is a reporter, spontaneous but emotionally damaged, appearing selfish to others and deeply alienated. She is a middle-aged woman with a history of abrupt career and life changes. Early in her adult life she lost her scholarship to the University of Nevada and quickly became a reporter for the Los Angeles Herald Examiner. Four years later, she married into money and became a wealthy Los Angeles social butterfly with an only child. After surviving a round of surgery for cancer, she left her husband and worked for the Washington Post covering the 1984 presidential election. Then she suddenly quit that job and sought out her estranged and ailing father in Florida. At that point she uncovers a wide-ranging international arms conspiracy that will lead to an assassination.

Treat Morrison is an upper-level government official. He investigates Elena's documents and then becomes romantically involved with her.

Richard McMahon is Elena McMahon's father, who smuggles arms to Central American countries. He hopes for a big payoff but is involved in something more sinister than what he reveals to his daughter. When he falls ill, she takes his place to complete an arms drop and has her ex-husband hide with their child.

The unnamed narrator serves only to describe the events of 1984 and introduce the reader to Elena McMahon.

Wynn Janklow is Elena McMahon's ex-husband, wealthy and living in Los Angeles. Some may view him as a villain.

The supporting characters are two minor villains. Bob Weir is a source for Elena McMahon who turns out to be central to the arms deal and involved in many other parts of a conspiracy. An unnamed Salvadoran is Weir's partner in crime.