A gunfight erupts on the streets of New York, where military policemen pursue a band of spies. Only the intervention of Wonder Woman prevents innocent people being hurt or killed. Though the Amazon's actions kept vitally important papers out of the hands of the Nazis, she is reproached by Congressman Thomas Cole for interfering in matters of national security.

Changing to her Diana Prince identity, our heroine joins Steve Trevor in the warehouse where the top-secret project they are assigned to is housed, the very project from which the spies stole the papers. That theft has compromised the project's security. Because of Trevor's friendship with Wonder Woman, Cole demands the officer's security clearance be suspended until the Amazon has accounted for herself before Cole's Congressional committee. En route to report to General Blankenship about this turn of events, Steve is nearly killed when his sabotaged jeep crashes. Rescued at the last second by Wonder Woman, Trevor decides to investigate why Cole is so anxious to have the two of them away from the project.

On Paradise Island, Queen Hippolyte decides to order Diana home to protect her from the dangers of Man's World… and to separate her from Steve Trevor. Before she can act on her decision, she is summoned to an audience with Aphrodite, divine patron of the Amazons. The Goddess of Love forbids Hippolyte to recall Wonder Woman because her mission of peace is not yet accomplished, warning that “the gods of evil plot with the fate of the Earth this very moment! Events involving you-- your daughter and the entire world are about to transpire,” events which will be Princess Diana's “trial by fire.”

Returning to the now-deserted warehouse, Wonder Woman is ambushed and taken prisoner by a shadowy figure in a crimson stormtrooper uniform. Boasting that his previous encounter with his captor taught him her weakness, he welds her bracelets together before disappearing into the night with her.

Steve and Etta Candy's concern for the missing Yeoman Prince is forgotten when they are ordered to close up their New York office and return to Washington.

The halls of the extradimensional “Home of the Gods” rings with the sound of combat as Mars, Greco-Roman God of War, and Thor, Norse God of Thunder, spar. Hercules and other onlookers cheer for one or the other. As Aphrodite and Athena, Goddess of Wisdom, worry that the worldwide war on Earth is increasing Mars' strength, he forces Thor to concede defeat. Later, he meets with his trio of advisors ― the Duke of Deception, the Earl of Greed and Lord Conquest ― and tells them that he will soon achieve total mastery of “the Earth and all the gods they worship,” thanks to his latest agent. As long as this agent possesses a certain talisman, the Disc of Mars, he will be invincible… and the war will continue. Overhearing the God of War's plans, Athena and Aphrodite contact Hippolyte once more in the hope that Wonder Woman can locate Mars' agent before it is too late, unaware their foe is already taking steps to destroy the Amazon.

Adolf Hitler, Mars' most enthusiastic pawn, is displeased with his operative's failure to carry out his mission despite his compensatory capture of Wonder Woman. He decides to try another approach and turns to Baroness Paula Von Gunther, “cruel and fully qualified Gestapo agent-- and slave queen of a thousand girls!” She tells Der Führer that the small box in her hand contains the key to making the two of them invincible.

In a derelict building not far from where Steve Trevor is testifying before Tom Cole's committee, an imprisoned Wonder Woman comes to. Cole declares the hearing recessed until the super-heroine can be subpoenad and places Steve on “extended leave.”

A few minutes later, a new super-hero clad in World War I aviation gear bursts onto the scene: the Bombardier, whose hands emit a strange explosive energy that gives him super-powers, including flight. The same ‘inner voice’ that grants him his powers tells the human rocket where the missing Amazon is being held. He bursts into the warehouse but Wonder Woman, mistakenly concluding he is the one who fused her bracelets, attacks the neophyte hero. As proof of his good intentions, he seperates her bracelets. Though declining to give his true name, the Bombardier tells of his experiences as a fighter pilot in the early days of the war and of being saved from certain death by a voice, which promised him “strength will be yours in time of need.” He had believed it a hallucination until the voice came to him again and bade him rescue Wonder Woman. She wonders if he has been sent by her mother before declaring it “unthinkable” that Hippolyta would choose a man as her agent.

The Amazon queen, meanwhile, is commanded by Aphrodite and Athena to send Princess Diana in search of the warrior bearing the Disc of Mars. Convinced by the goddesses' warnings that Paradise Island can no longer remain above the fray, she orders the Amazons to prepare for war. Her timing is faultless. Mars orders his Harpies and the Valkyries, under his control since his defeat of Thor, to attack the Amazon homeland.

No sooner have Wonder Woman and the Bombardier flown away in her invisible plane than her captor ― who stands revealed as Helmut Streicher a.k.a. the Red Panzer ― discovers her escape. Diana is concerned when she cannot reach Paradise Island by mental radio. Bombardier receives a psychic message from the voice to return to Washington and his civilian identity. His request reminds his companion of her duties as Diana Prince.

The Panzer is confronted by Paula Von Gunther, who offers him a chance to turn aside Hitler's displeasure with the Nazi super-villain's repeated failures by helping her complete her secret project.

Reporting to General Blankenship's office, Yeoman Prince explains that she was helping Wonder Woman track down the spy ring. Blankenship decides that “Project Judgement” can no longer be held up by a Congressional investigation and reaches for the phone to call the White House. Before he can dial, he and his staff are summoned to the War Room. General Katz and Congressman Cole tell them that the delays to “Project Judgement” may have decided the outcome of the war. Even now American forces are falling back before a German advance, news that secretly delights Cole, who muses that “now I can meet my destiny face to face!” Wonder Woman flies to the front and joins the desperate battle. The Bombardier arrives shortly after, his explosive powers devastating the German troops.

Von Gunther and Streicher inform Hitler by radio that the “ultimate weapon” is only hours away from completion. The baroness cold-bloodedly executes her slave girls before she and the Panzer board a submarine bound for the Fatherland.

The furor of the battlefield makes Mars so powerful that even the Goddess of Love is infected with war madness. Her rage and hatred mirrors that on Earth and on Paradise Island, where the Amazons are slowly retreating before their enemies. But Aphrodite is no warrior. Mars overpowers and humilates her before a jeering Hercules and the War God's other cronies.

Wonder Woman and the Bombardier fight valiantly against tremendous odds but despite their efforts, the Germans break through the American lines. The heroic duo step back from the fighting to assess their situation. The Bombardier removes his goggles to reveal the face of Thomas Cole. Racked with guilt over his bloodthirst during the battle and the role his committee's investigation of Project Judgement played in this defeat, he apologizes for questioning the Amazon's loyalty. They hurry back to Washington. The congressman orders Steve Trevor back to active duty and grants Wonder Woman “full status as an operative of the United States Government.” Their task: destroy Nazi Germany's version of Project Judgement before it can be activated.

A survivor of Baroness Von Gunther's slave massacre tells Steve and Diana all she knows of the Red Panzer and her mistress' plans, even as the villains report to Hitler. En route to Germany in Wonder Woman's plane, the Bombardier flying alongside, Trevor tells his Amazon companion about Project Judgement, a sonic cannon known as the “cyclosonitron” with destructive capabilities akin to those attributed to the archangel Gabriel's Horn of Judgement.

Reaching Berlin, the intrepid trio burst into the chamber where Hitler's cyclosonitron is about to be fired. They overcome the Panzer and Von Gunther. While Bombardier chases the fleeing Führer, the Amazing Amazon desperately searches her foes for the Disc of Mars. Realizing Hitler himself must bear the talisman, she joins the chase but the heroes are too late. The dictator fires the cyclosonitron.

The Harpies and Valkyries break off their attack despite their impending victory, leaving the battered Amazons wondering what Mars will do next.

Wonder Woman and the Bombardier combine their super-powers to destroy the sonic weapon before its devastating effects can spread far. It is only in the quiet aftermath of the cannon's explosion that Diana realizes that the human rocket's destructive super-powers and bloodlust in combat mark him as the wielder of the Disc of Mars. His secret exposed, Mars takes control of Bombardier and tries to kill the Amazing Amazon. Wonder Woman is able to get close enough to take the talisman from Cole's costume and destroy it. Freed of the War God's domination and stripped of his powers, Congressman Cole retains no memory of his brief career as a super-hero.

On Paradise Island, Hippolyte learns from Aphrodite that Diana's victory has weakened Mars enough that the Allies' chances of winning the war are greatly improved. The Amazon queen is proud of her daughter and approves her remaining in America for as long as it takes to achieve final victory over the Axis.