NOW, BY MY HAND, SHALL DIE A VILLAIN!

At the Avengers' monthly meeting, Thor presides as acting chairman and adjourns the session after routine business is concluded. The heroes go their separate ways to enjoy a rare evening off. Giant-Man and the Wasp plan a dinner date, but Janet, too hungry to change into civilian clothes, simply hides her costume beneath a long overcoat. Thor transforms back into Dr. Donald Blake before leaving for the city, while Captain America changes into Steve Rogers and conceals his shield inside a large artist's portfolio. Iron Man remains behind, claiming he wants to inspect the mansion's equipment, though in reality Tony Stark secretly recharges the chest device that keeps him alive, determined to protect the secret of his dual identity.

Far away in the Amazon jungle, Baron Zemo emerges from months of hiding to begin his long-awaited revenge against the Avengers. Determined to destroy his enemies once and for all, he devises an elaborate trap aimed not at the heroes themselves, but at their weakest link. Confident that Captain America's loyalty to Rick Jones can be exploited, Zemo dispatches his agents to set the scheme into motion, convinced that this carefully orchestrated plan cannot fail.

Back in New York, Steve Rogers struggles to write a letter to Colonel Nick Fury, expressing his hope of joining SHIELD as a counter-espionage agent and finally earning an honest living outside of being Captain America. After mailing the letter, Steve unexpectedly spots the Enchantress and the Executioner riding through the city in a passing automobile. Realizing they are up to no good, he races after the speeding car, using his remarkable agility to leap through traffic. Just as he begins to close the distance, the Enchantress senses she and the Executioner are being followed and casts a spell that causes Steve to lose his balance, allowing the villains to escape.

Later, the Enchantress and Executioner receive a transmission from Baron Zemo, who announces that the first stage of his master plan is underway. Although the Executioner confidently predicts victory, Zemo warns his allies not to underestimate the Avengers, reminding them that the team has survived every previous attempt to destroy them. Meanwhile, Captain America returns to Avengers Mansion and immediately calls an emergency meeting after reporting his encounter with the evil Asgardians.

As the Avengers prepare for trouble, they suddenly hear the roar of aircraft overhead. Racing outside, they witness Rick Jones being lifted helplessly into the sky by an invisible tractor beam connected to a passing airplane. Thor and Iron Man launch into pursuit, but Zemo's agents drop powerful concussion mines that explode beneath them, temporarily stunning both heroes. Giant-Man quickly enlarges himself and catches his falling teammates before they crash, while Captain America passes his shield to the giant hero, who uses it like a projectile against the fleeing aircraft. Although the throw is perfectly aimed, the plane's protective force field deflects the shield harmlessly. Unknown to the kidnappers, however, the Wasp secretly sneaks aboard the aircraft and overhears that Baron Zemo himself ordered Rick's abduction.

Determined to rescue Rick, Iron Man remotely summons one of Tony Stark's advanced hunter planes while Captain America blames himself for allowing his young partner to be captured. At the same time, another part of Zemo's elaborate plan unfolds as the Enchantress and Executioner use magic to free the Melter and the Black Knight from prison. Armed once again with their weapons and the Black Knight's winged horse, the villains receive orders to intercept the pursuing Avengers before they can reach Zemo.

The Black Knight soon attacks the Avengers' aircraft, using the unique weapons concealed within his lance. One device expands into a gigantic spinning ring of razor-sharp blades that wraps around the hunter plane, threatening to slice it apart. Thor bursts from the aircraft and smashes the deadly weapon with Mjolnir before engaging the Black Knight in an aerial duel. The villain skillfully lures Thor away, unknowingly leading him into the next stage of Zemo's coordinated assault.

Inside the damaged aircraft, the Wasp returns from the kidnappers' plane and reveals that Baron Zemo is behind the entire operation. Before she can fully explain, the Melter launches a surprise attack from the streets below, firing his melting ray at the aircraft. Iron Man leaves the plane to battle the villain, but the Melter cleverly manipulates the fight, tricking Iron Man into accidentally striking a rooftop water tower. As Iron Man diverts his attention to preventing the tower from collapsing onto innocent civilians, the Melter welds Iron Man's armored boots to the rooftop and prepares to unleash his full-powered melting beam against the helpless Avenger.

At the same time, the Avengers' aircraft suddenly becomes trapped by one of the Enchantress' magical force fields. With no other option, Giant-Man leaps from the immobilized plane, enlarging himself to an incredible one hundred feet tall before landing safely on the city rooftops. From his towering vantage point, Hank spots the Enchantress and the Executioner below and realizes they are responsible for immobilizing the aircraft. While the Wasp bravely attacks the villains, the Enchantress magically paralyzes her wings. Giant-Man arrives just in time to drive the villains away and rescue Janet before they can capture her.

Once the magical spell is broken, Captain America realizes Rick's kidnapping is merely bait designed to lure him into Zemo's grasp. Determined to end their long rivalry once and for all, he flies alone to the Amazon jungle despite the risks. There, Zemo immediately launches a massive anti-aircraft barrage against Cap's approaching aircraft. Captain America destroys the gun emplacements with rockets, only for Zemo to raise Rick Jones inside a glass prison directly into his line of fire. Although the cage is shattered, Rick survives unharmed, revealing that Zemo intended to trick Captain America into accidentally killing his own partner.

Meanwhile, the battles continue in New York. Thor abandons his duel with the Black Knight when he realizes Iron Man's life is in danger, intercepting the Melter's devastating beam with Mjolnir. Iron Man frees himself from the rooftop while the Melter retreats to regroup with his allies. As the villains attempt to escape in a car, Giant-Man blocks the roadway with his gigantic hand, crushing the vehicle beneath its own momentum. The Black Knight attacks the towering Avenger, but Giant-Man cleverly uses the flattened automobile as an improvised shield against the villain's exotic weapons.

Both sides soon gather for a final confrontation. Iron Man notices Captain America is missing, while the Executioner attempts to delay the battle by reminding Thor of his oath not to endanger innocent mortals. Thor refuses to be manipulated, declaring that evil must be stopped regardless of the risks, and rallies his teammates with the cry, "Avengers Assemble!" Even so, the villains manage to avoid a decisive defeat as events in the Amazon rapidly reach their climax.

Deep within the jungle, Captain America and Rick reunite after Rick escapes his shattered prison. Ignoring Rick's warnings that Zemo possesses overwhelming weapons and manpower, Captain America presses forward, declaring that justice itself is his greatest weapon. The longtime enemies finally confront one another face-to-face in a battle years in the making.

As the duel intensifies, Captain America deliberately throws his shield wide of its target, striking a rock formation instead of Zemo himself. The collapsing boulders separate Zemo from his soldiers, forcing the villain to face Captain America alone. When Zemo fires his deadly disintegrator ray, Captain America angles his shield to reflect the sun directly into Zemo's eyes. Blinded, Zemo accidentally fires into the rock wall supporting the cliff above him, triggering a massive landslide. Captain America protects himself behind his shield, but Zemo is buried beneath the avalanche and killed by his own actions.

With Baron Zemo finally defeated, Captain America quietly reflects that Bucky's death has at last been avenged. As he and Rick Jones leave the jungle together, Cap acknowledges that justice has finally caught up with his greatest enemy, bringing an end to one of Marvel's earliest and most enduring rivalries while closing a major chapter in the history of the Avengers.