The story is set on Themyscira, a hidden island created by goddesses as a sanctuary for the Amazons, immortal female warriors reborn after dying gloriously in battle. Diana, the teenage daughter of Queen Hippolyta, is the only Amazon who was not reborn through combat but created from clay, a fact that makes her an outsider among her sisters. Tekmessa (Tek), Hippolyta's closest advisor and a general, mocks Diana with the nickname "Pyxis," a small clay pot, underscoring her fragile origins.
During a footrace at the Nemeseian Games, Diana spots a schooner exploding offshore. She abandons the race, leaps from the cliffs, and crosses the magical boundary shielding the island to pull a drowning girl named Alia from the wreckage. Bringing a mortal to Themyscira is punishable by permanent exile. Diana hides Alia in a cave and returns to the Epheseum, the Amazon city.
The island immediately begins to suffer. Diana's friend Maeve collapses with a mysterious fever, the first illness Themyscira has known, and earthquakes shake the ground. Suspecting Alia's presence is the cause, Diana consults the Oracle, who reveals that Alia is a Warbringer: a descendant of Helen of Troy whose bloodline was sired by Nemesis, the goddess of divine retribution. In every generation, a Warbringer catalyzes devastating war. If Alia's power reaches its apex at the start of Hekatombaion, the first month of the ancient Greek calendar, global conflict will become inevitable. The Oracle shows Diana a vision of her sisters dead on a future battlefield, then explains that if Alia bathes in the spring at Therapne, near Helen's tomb in Greece, before sunset on the first day of Hekatombaion, the Warbringer line will be broken forever. Despite the Oracle's warning that she is untested, Diana resolves to attempt the quest.
She returns to the cave and leads Alia through the Armory, where iron bracelets animate and clasp around Diana's wrists. Diana also claims a golden lasso and a heartstone, a star-shaped ruby that serves as a navigational compass. She builds a raft and sails through the boundary, but Alia's overwhelming desire for home overpowers the heartstone. Instead of Greece, they emerge in New York Harbor. A full week has passed in the mortal world, leaving fewer than six days before Hekatombaion.
In Manhattan, Alia leads Diana to an emergency supply bag kept by her older brother Jason. Jason, Alia's twenty-one-year-old brother and heir to the Keralis fortune, tracks them through a burner phone's signal and breaks into their hotel room. Diana pins him before Alia identifies him. When Diana mentions the Warbringer, Jason's skepticism vanishes. He reveals that their late parents, renowned bioengineers, left behind secret research documenting the Warbringer bloodline, including a scroll tracing descendants of Helen through centuries of wars. Headlines on Jason's phone confirm escalating global violence, proving Alia's power is already building.
Jason agrees to fly them to Greece but insists they first attend a Keralis Foundation gala at the Metropolitan Museum of Art. Alia's best friend, Poornima "Nim" Chaudhary, a bold aspiring designer, arrives to help prepare. At the gala, Jason speculates to Diana that Alia's power may have caused the car accident that killed their parents. Alia overhears and is devastated. Diana comforts her, and they swear an Amazon oath of mutual protection: "Sister in battle, I am shield and blade to you." Alia extracts a grim promise: If they fail to reach the spring, Diana must kill her.
Armed soldiers attack the gala, hunting the Warbringer. Diana discovers the full extent of her combat abilities, deflecting bullets with her bracelets and hurling furniture as weapons. Nim's companion, Gemma Rutledge, is killed. Diana topples the ancient temple exhibit to create a barricade and rams open blocked exits with a pillar. The group escapes to Central Park, where the Keralis pilot crash-lands the company jet on the Great Lawn, and they flee aboard it.
The group learns the attackers belong to international organizations that hunt Warbringers. Nim and Theo Santos, the son of Jason's godfather, insist on staying with Alia. Over Greek airspace, soldiers breach the fuselage. The pilot is killed. Jason is sucked out the door but reappears clinging to the wing with impossible strength. The group parachutes out before the jet is destroyed.
On the ground in Greece, Diana uses her lasso, which compels absolute truth, to force Jason to admit he carries the enhanced blood of Menelaus and the Spartan kings, granting him superhuman strength he has hidden his entire life. The gods of battle begin manifesting as Alia's power escalates. Eris, the goddess of strife, possesses Nim and tries to strangle Theo; Phobos, the god of panic, possesses Theo. Diana drives Phobos back with the lasso.
The group steals a car and drives south. Deimos, the god of terror, runs them off the road with a chariot disguised as a truck. They camp by a waterfall, where they play a truth game with the lasso. Nim reveals that a girl named Alicia Allen kissed her and then denied it; Alia accidentally confesses she once wrote Theo a love letter. Later that night, Diana and Jason share a kiss on a mountaintop.
They arrive at the Menelaion, Helen's tomb near Therapne, but find no spring, only overgrown ruins. Eris and the twin gods appear, filling the air with the deafening din of war. Diana swings the lasso in a widening arc to drive them back. In the sudden quiet, Alia hears the ghostly voices of Helen's girlhood companions singing and realizes the spring is not at the tomb but at the river Eurotas below, where Helen once laid a wreath at a great plane tree.
Before they can reach the water, Jason seizes Alia and reveals his betrayal. He never intended to let her reach the spring. He has been stalling, secretly commanding a private army of soldiers enhanced with ancient hero DNA. His vision is to let the Warbringer's power trigger global war, then deploy electromagnetic pulses to disable modern weapons and unleash mythological monsters for his super-soldiers to fight, uniting humanity against common foes. He has also been synthesizing a serum from Diana's DNA, collected from cells she left at his penthouse.
Diana refuses to join him. Jason unleashes Pinon, a monstrous hybrid with a woman's torso and a scorpion's body, engineered to drain blood. In the ensuing battle, a soldier breaks Nim's neck, Theo is mortally wounded, and Pinon drains Diana's blood until she dies.
In death, Diana encounters the goddesses who created Themyscira. They offer her rebirth as a full Amazon, her crime erased. Diana refuses, asking instead that Nim and Theo be resurrected so she can continue the fight. She wagers her immortality: If she dies again in the mortal world, she will pass permanently to the Underworld. The goddesses accept and resurrect all three.
Revived, the group counterattacks. Theo hacks Jason's network and destroys his genetic research. Nim prepares grenades to destroy the lab truck and Pinon's cage. Alia deliberately wields her Warbringer power for the first time, turning Jason's soldiers against each other by amplifying their aggression. Diana fights Jason in single combat. He injects himself with the serum, but the Amazon blood bond overwhelms him: Every blow he strikes against Diana, he also feels, along with the accumulated pain of every fallen Amazon. He collapses. Diana refuses to grant him an honorable death.
Diana carries Alia to the river as the last light fades. Alia plunges into the spring beneath the plane tree. The sounds of global warfare build to a roar, then break and recede. Three golden figures appear: Helen and her twin brothers, the Dioskouroi, legendary warriors and guardians in Greek myth. Helen lays a wreath against the tree and fades. The Warbringer line is broken forever.
Diana says goodbye to her friends and uses the heartstone to return to Themyscira, arriving only hours after she left, as time passed differently on the island. Hidden in the bramble walls of the Oracle's temple, she watches Hippolyta and Tek consult the Oracle, who tells them the crisis has passed. The Oracle reveals to Diana that the goddesses engineered her quest, provoking her with doubt so she would fight harder. Diana returns home, battle-tested and certain of her identity as an Amazon, knowing the mortal world will one day call her back.