In present-day Paris, Diana Prince, curator for the Louvre’s Department of Antiquities, receives a World War I-era photographic plate couriered by Wayne Enterprises and recalls her past.
Diana was born and raised on the hidden island of Themyscira, home to the Amazon race of warrior women created by the gods of Mount Olympus to protect humankind against the corruption of Ares, the god of war. In the distant past, Ares slew all his fellow gods, but his mortally wounded father, Zeus, struck him down. Before succumbing to his injuries, Zeus left the Amazons a weapon capable of killing his renegade son: the “Godkiller”, which Diana believes to be a ceremonial sword. Hippolyta, Diana’s mother and queen of the Amazons, believes that Ares will never return and thus forbids Diana from training as a warrior, but Diana and her aunt, General Antiope, defy the queen and begin training in secret. When the two are discovered by Hippolyta, Antiope convinces her sister to allow Diana’s training to continue.
As a young woman, Diana rescues Captain Steve Trevor, a pilot with the American Expeditionary Forces, after his plane crashes off the coast of Themyscira. The island is soon invaded by the landing party of a German cruiser pursuing Steve. The Amazons engage and kill all the German sailors, but Antiope dies intercepting a German bullet meant for Diana. Interrogated with the Lasso of Truth, Steve reveals that World War I is raging in the outside world, and that he is an Allied spy. He stole a notebook from the Spanish chief chemist Isabel Maru known as “Doctor Poison”, who is attempting to engineer a deadlier form of mustard gas under the orders of General Erich Ludendorff. Believing Ares is responsible for the war, Diana arms herself with the ceremonial sword and leaves Themyscira with Steve to find and destroy Ares.
When the two arrive in London, they deliver Maru’s notebook to Steve’s superiors, including Sir Patrick Morgan, who is trying to negotiate an armistice with Germany. Diana translates Maru’s notes and reveals that the Germans plan to release the deadly gas at the warfront. Although forbidden by his commanders to act, Steve, with secret funding from Sir Patrick, recruits spy Sameer, marksman Charlie, and smuggler Chief to help him and Diana infiltrate enemy lines and prevent the gas from being released. When the team reach the Western Front in Belgium, they are halted by enemy machine guns, but Diana pushes alone through the German lines and rallies the Allied forces behind her to liberate the village of Veld. The team briefly celebrates and takes the group photograph from the beginning of the film. Later that night, Diana and Steve shared a kiss and it is implied that they spent the night together.
The team learns that a gala will be held at the nearby German High Command. Steve infiltrates the party, intending to locate the mustard gas and destroy it. Diana, however, believes Ludendorff is Ares and that killing him will end the war. Steve stops her to avoid blowing their cover and jeopardizing the mission. Ludendorff unleashes the mustard gas on Veld, killing all of its inhabitants. Diana blames Steve for intervening, and pursues the general to a military base where the gas is being loaded into a bomber bound for London. Diana fights and kills Ludendorff, who is physically enhanced by another of Dr. Maru’s gases, but is crestfallen when his death does not stop the war.
Sir Patrick appears and reveals that he is actually Ares. He tells Diana that although he has subtly given humans ideas and inspirations, it is ultimately humankind’s decision to cause war and violence. After destroying the ceremonial sword, Ares reveals that Diana is the true “Godkiller”: she is the daughter of Zeus and Hippolyta, and thus Ares’ half-sister. Ares attempts to convince Diana that humanity is inherently corrupt, and that she should help him destroy humankind to restore paradise on Earth. While the two battle and the rest of Steve’s team destroy Dr. Maru’s laboratory, Steve sacrifices himself by piloting the bomber carrying the gas to a safe altitude resulting to a fiery explosion into the sky to prevent the gas from reaching its destination. Ares attempts to harness Diana’s rage at Steve’s death by convincing her to kill a helpless Dr. Maru, but Diana’s memories of Steve inspired her that humans have good within them and she spares Maru out of mercy before overpowering and destroying Ares. Back in London, the nation celebrates the end of the war.
In the present day, Diana sends an e-mail to Bruce Wayne thanking him for the photographic plate of her and Steve and reaffirms her mission to protect all life as Wonder Woman.