An insecure ruler, prone to acting on his whims and accustomed to a lifestyle of outrageous luxury and recreation, loves nothing more than dining and celebrating with the wealthy elite who support him. He declares a nationwide holiday, many months devoted to opulence and debauchery.
The king's holiday is a celebration of deregulation.
The king has a closed circle of male sycophantic advisors, all of whom are outwardly subservient to the king (but behind the scenes, know that he is easily manipulated by flattery). They call for the queen to perform erotically for them. Vashti rejects the king’s crass locker-room talk.
Vashti, the king’s first wife and a victim of his sexual predation, disappears from the story, never to be heard from again. The king is excited to marry a new and younger wife, perhaps an immigrant to Shushan. In essence, the king holds a "Miss Persia" pageant which he owns (and of course has no reservations taking advantage of the young hopeful contestants).
A young Jewish woman named Hadassah—but who goes in polite society by the less ethnic-sounding name Esther—against all odds ends up in the royal household. To ensure populist approval, the king cuts taxes and distributes favors among his supporters.
Mordecai, who like many Jews has achieved great success in Persia, uncovers a plot and saves the king’s life. When Mordecai refuses to bow to Haman, Haman issues a decree of annihilation against the Jews. He seduces the king with talk about how a third-column of immigrants threatens real Persians. It is time to put Persia First; Haman posits that a sinister cabal of Jews who follow only their own protocols is holding the nation back from being great. Antisemitic incidents rise; it’s worse than it’s been in anyone’s recent memory.
There is no official response from the administration.
Mordecai petitions Esther to take a stand. Esther agrees, but notes that everyone in the king’s inner circle knows that he is very prone to impulsiveness and lashing out, so who knows what will happen?
Nevertheless, Esther persisted. She invites the king and Haman to a most exclusive royal banquet.
Meanwhile, despite the air of general prosperity, Haman is incensed that a foreigner—Mordecai—continues not to know his own place. He plots to have Mordecai killed.
The king, unable to sleep, instructs an aide read to him (rather than actually reading himself). There, he discovers that even though Mordecai had saved his life, he had not remembered to thank him. Haman is forced to lead Mordecai in a royal procession through the capital. Humiliated, Haman mourns for his once-great country.
Haman, the king, and Esther have their private banquet. She reveals Haman’s plot and the king, enraged, declares that his friend and former advisor has clearly lost his mind. Haman is publicly executed.
However, the edict calling for the destruction of the Jews remains in effect. The arcane founding laws of the country have not evolved with current technology, so there is no legal way to prevent a massacre from happening. An edict calls upon the Jews to defend themselves against their enemies.
The resistance is successful. The Jews find success unlike any they have received in any other kingdom. Esther and Mordecai are ensconced in power. In their opulence, wealth, and feasting—and in becoming accustomed to violence committed in their name, always in self-defense, of course—the Jews of Shushan even start to act just like the Persians did at the beginning of the book. 
A holiday is declared to remember these events. Part of the observance is a reminder to give gifts to poor people, who previously have been invisible in this story.
An annual day of irreverence and celebration—called “Purim,” to remind us how so much of our fate relies on chance—is established.
 Esther 1:3
 1:10, 1:14
 1:11, Esther Rabbah 3:13
 Esther Rabbah 7:4
 Esther Rabbah 6:2
 8:17, 9:4
 9:5, 9:16