In the opening scene in modern day Paris, France, Diana Prince (Gal Gadot) visits the Louvre as a van from Wayne Enterprises pulls up. She receives a briefcase sent by Bruce Wayne. Inside is an old photograph of Diana alongside four men during World War I. With the picture is a note from Bruce saying he would like to hear the story behind the picture.
Diana: I used to want to save the world. This beautiful place. But I knew so little then. It is a land of beauty and wonder, worth cherishing in every way. But the closer you get, the more you see the great darkness simmering within. And mankind? Mankind is another story altogether.
As a child, Diana (played by Lilly Aspell) grew up on the island of Themyscira alongside the mighty Amazons, an all-female warrior clan. She watches the warriors training on the field under General Antiope (Robin Wright). Diana wants to be a fighter like the rest of the Amazons, but her mother, Queen Hippolyta (Connie Nielsen) forbids her daughter from training. Hippolyta takes Diana and tells her the story about the gods.
Zeus ruled over the heavens and looked upon mankind with high regards, but Ares, the god of war, sought to corrupt mankind and lead them to tear each other apart in battle. The other gods fought back against Ares, but he killed all of them. With his dying breaths, Zeus cast Ares down into the world of man and then forged a weapon that can destroy Ares once and for all. He also gave the Amazons their home on Themyscira to hide them from the rest of the world.
Hippolyta shows Diana the powerful sword known as the God Killer. With it, Ares can be killed, but Hippolyta hopes there will not come a time for Diana or anyone else to wield it. Antiope convinces Hippolyta to let her train Diana, wanting her to be ready to face Ares, because they all know he's still out there. Hippolyta reluctantly agrees. Through the years, Antiope subjects Diana to harsh and intense training in the field.
As she reaches adulthood, Diana continues training to be as fierce as the other Amazons. During one session, Antiope pushes Diana hard with her swordplay, leading Diana to defend herself by deflecting the sword with her gauntlets. This causes Antiope to fly back and hurt herself. Diana shows great remorse for hurting Antiope. She leaves in shame, but Antiope is far from upset.
Diana runs over to a cliff. In the distance, a plane passes through the barrier into Themyscira before crashing into the ocean. Diana dives into the water and swims toward the plane. A pilot named Steve Trevor (Chris Pine) is sinking as he cannot break himself free from his seat. Diana pulls him out of the plane and takes him to shore.
Diana: You're a man.
Steve: Yeah. I mean, do I not look like one?
German soldiers following Steve make it past the barrier as well.
The Amazons arrive as they find Diana with Steve, but also see the Germans. The Amazons ready their arrows, and the Germans aim their rifles. The arrows are launched and shots are fired. The Germans make it to the shore and battle the Amazons. Several Amazons are shot dead while the Germans get taken out easily. Antiope fires three arrows at once to kill three soldiers. One soldier aims his gun at Diana, and Antiope leaps in to take the shot. Diana rushes to Antiope's side. As she dies, she tells Diana it is her time to wield the God Killer.
Steve is interrogated before all the Amazons with the Lasso of Truth.
Hippolyta: What are you?
Steve: [tries to get around the question, but fails] I am a spy!
Hippolyta: What is your mission?
Steve: To stop the war.
Diana: What war?
Steve: The war to end all wars. Weapons far deadlier than you can imagine! Whoever you are, you are in more danger than you realize!
Steve explains to the Amazons about World War I and how he has learned of a sinister plan by Germany's General Erich Ludendorff (Danny Huston) and his chief chemist Dr. Isabel Maru, AKA Dr. Poison (Elena Anaya).
They are concocting a new bioweapon, which Steve claims is unlike anything he's seen before and tells the Amazons they are in more danger than they realize. Steve acted as a spy in the German army before stealing Maru's notebook and flying away with it as he destroyed the Germans' other planes until they followed him to the island. Diana realizes this must be the work of Ares.
Steve is allowed to bathe in the Amazons' fountain to replenish himself. Diana walks in and accidentally sees him nude.
Diana: What is that?
Steve: [finally realizing she was referring to his watch] That is a watch.
Diana: What does it do?
Steve: It tells the time. It tells you when to sleep, to eat.
Diana: You let this little thing tell you what to do?
Steve: What is this place? Who are you people?
Diana: We are a bridge to a greater understanding.
Still fearing that Ares is behind the ongoing war, Diana grabs her shield, lasso, and then takes the God Killer sword from its holding, along with her battle suit. She goes to tell Steve she will help him get home if he takes her to Ares.
The two head for the shore but are approached by Hippolyta and other Amazons. Diana is insistent that she goes out there to stop Ares and end the war.
Diana: I'm going, mother. I cannot stand by while innocent lives are lost. I'm willing to fight for those who cannot fight for themselves.
Hippolyta: You know that if you choose to leave, you may never return.
Diana: Who will I be if I stay?
Hippolyta: [gives Diana Antiope's tiara] This belonged to the greatest warrior in our history.
Hippolyta tearfully embraces her daughter one last time.
Hippolyta: Be careful in the world of men, Diana. They do not deserve you. You have been my greatest love. Today, you are my greatest sorrow.
As Diana and Steve depart, Menalippe approaches Hippolyta.
Menalippe: You should have told her?
Hippolyta: The more she knows, the sooner he will find her.
While sailing to London, Steve and Diana chat about the lack of men in Themyscira, marriage, sleeping arrangements, and sexual rituals.
Steve: Have you never met a man before? What about your father?
Diana: I had no father. My mother sculpted me from clay and I was brought to life by Zeus.
Steve: Well, that's neat.
Diana: I've read all 12 volumes of Clio's Treatises on Bodily Pleasure.
Steve: All 12, huh?
Steve: Did you bring any of those with you?
Diana: They came to the conclusion that men are essential for procreation, but when it comes to pleasure . . . unnecessary.
After shooting an officer for reporting a lack of progress, Ludendorff meets with Dr. Maru.
Dr. Maru: General.
Dr. Maru: Not enough. It is over, General. Germany is giving up. Von Hindenburg has recommended the Kaiser sign the Armistice. We have run out of time.
Ludendorff: As soon as the Kaiser sees the newest weapon, he will not sign the Armistice.
Dr. Maru: But without my book . . .
Ludendorff: We will get your book! It is YOU I believe in, not it! I know that you can and will succeed. It is what you were put on this Earth to do.
Dr. Maru: Something did come to me last night. A different type of gas. For you. To restore your strength.
Dr Maru opens the gas and Ludendorff breathes it in, giving him super-strength. One of Dr Maru's screwed-up notes is mysteriously pushed towards her. She reads it.
Dr. Maru: I've got it. I've got it! And if it's what I think, it's going to be terrible.
Diana and Steve arrive in London as she looks over the all gray city.
Diana: It's hideous!
Steve: Yeah, it's not for everybody.
Diana: [sees a couple] Why are they holding hands?
Steve: Uh. . . Probably because they are together.
Diana tries to hold Steve's hand.
Steve: No, no, no. We're not together. I mean, in that way.
Diana: To the war.
Steve: Technically, the war is that way. But first we got to go this way.
Diana: Awww, a baby!
Steve: No, no. No babies. That one is not made of clay.
The two meet with Steve's secretary, Etta Candy (Lucy Davis).
Etta: I'm introducing myself. It's Etta Candy. I'm Steve Trevor's secretary.
Diana: What is a secretary?
Etta: Oh, well, I do everything. I go where he tells me to go, I do what he tells me to do.
Diana: Well, where I'm from that's called slavery.
Etta: I really like her.
Before they can deliver Maru's notebook to Steve's superiors, they find Diana an appropriate outfit to wear so she can blend in for the time.
Steve: Where is she?
Etta: Well, she's trying on outfit number 226.
Steve gives Diana glasses to wear.
Etta: Really, specs? Suddenly she's not the most beautiful woman you've ever seen?
Etta: The sword doesn't go with the outfit.
Steve: At all.
Diana and Steve are then cornered by some men in an alley. They draw their guns, but Diana beats them all down, even letting Steve punch the last guy out.
Diana and Steve head on over to a meeting held by Sir Patrick Morgan (David Thewlis), who is planning to negotiate an armistice with Germany. The men in the room are immediately distracted by Diana's presence. Steve is forced to take her outside.
Later, he presents Sir Patrick with the notebook.
Diana: I am Diana, Princess of . . .
Steve: Prince! Diana Prince!
Since the writing is in Sumerian, Steve has Diana (who speaks hundreds of languages) translate it for the other men. They learn that Ludendorff and Maru are planning to create a new kind of hydrogen-based mustard gas that would be far more lethal to the soldiers. After hearing that the British general is planning to send his troops to the Western Front and go in to most likely get killed, Diana becomes enraged and tells the general that a good leader would fight alongside his men.