This act serves to introduce the main characters — Antony, Cleopatra, and Octavius Caesar; it also outlines the main forces which motivate each of them. The first scene is set in Alexandria, where two of Antony's men, Demetrius and Philo, describe the lovers' relationship. Caesar appears in a later scene, and we see how he perceives Antony and Cleopatra's relationship. In addition, his comments about Antony reveal a great deal about his own character. We also have ample evidence in this act that Antony and Cleopatra are deeply in love, but Antony does not realize the tragic possibilities of their infatuation, yet he is torn by divided loyalties. In short, this first act sets out what the relationships are among the main characters, and it establishes the basic conflicts that dominate the rest of the play: first, Antony and Cleopatra and their love for one another; and second, Antony's rivalry with Caesar.
In this act, Shakespeare accelerates the inevitable final conflict between his primary characters. Pompey, an insurgent force against Rome, has become enough of a threat to the Roman Empire that the triumvirs are forced to form a truce in order to present a united front. Antony and Caesar decide to resolve the fighting among themselves; this new "alliance" is to be cemented by the marriage of Antony and Octavia, Caesar's sister. When Cleopatra finds out that Antony has married, she is devastated by the news. But she resolves not to give up Antony so easily. In the meantime, even while Antony pledges his loyalty to Octavia, his thoughts have returned to Egypt and Cleopatra.
Most of the main events of the play have their beginnings in this act. It begins with the continued efforts on Antony's part to work on behalf of Rome and regain his stature in the world of politics and war. But before long, he tires of the pursuit of power in Rome and decides to return to Egypt.
Octavia accompanies Antony to Athens, but she returns to Rome alone after Antony decides to return to Cleopatra. Octavia's disgrace gives Caesar sufficient reason to hate Antony even more than he already does, and he vows revenge. Octavia's discovery that Antony is glorifying Cleopatra and her children, one of them the illegitimate son of Julius Caesar, provides enough of an excuse for Caesar to declare that both Antony and Cleopatra are traitors. War begins, and Antony's forces are defeated; the rest of the play focuses, thus, on the aftermath of this battle and its effect on the love between Antony and Cleopatra.
Antony is at first despondent over his defeat. He places the blame on Cleopatra, who fled with her ships. He jeers that she will desert him for Caesar, just as some of his troops already have. She convinces him that he is wrong, and they courageously make one last attempt to defeat Caesar. They win a battle, but their victory is short-lived, and finally they are absolutely defeated. Again, Antony doubts Cleopatra's loyalty, and so she flees to her monument, the tomb where her body is to be buried after her death. She hopes to make Antony see the error of his doubts about her by sending him word that she is dead. Antony suffers great remorse and falls upon his sword. He does not die immediately, however, and he is taken to the monument, where Cleopatra is waiting for him. They spend his final moments together, and Cleopatra is left to face the Romans alone.
This final act concentrates on Cleopatra's last hours, as she negotiates with the Roman victors. Caesar has promised that she will be treated with honor in Rome, but she has good reason not to believe him. One of Caesar's officers, Dolabella, warns her not to put her faith in Caesar's promises. Cleopatra resolves to die rather than be taken captive to Rome, and she and her women have a basket of poisonous snakes smuggled to them in order to commit suicide. Thus, both Antony and Cleopatra die and they ultimately deprive Caesar's final victory of its full glory, as he finally acknowledges.