The Avengers stare at their now destroyed lab, thanks to their earlier battle against the Triumvirate of Terror. Wasp and Goliath hope that Tony Stark has got enough money to repair it. Hercules notices something wrong with Wanda, who claims she’ll be alright in a moment. Pietro worries about his sister but she claims she’ll be fine. Hawkeye surprisingly agrees with everyone and also notices she isn’t looking too well.
While the Avengers start repairing the equipment they can, Wanda admits to herself she isn’t fully recovered from the battle, hoping that by helping out she soon will be. Hank notices Hercules helping out and suggests he takes it easy, as he is only their guest, but Hercules thinks it’s only normal he does something to repay their hospitality.
Quicksilver uses his speeding powers to quickly put all of the mess out of their way and goes to relax a little on the video monitors, checking if it still works. On that very moment, Wanda gets very dizzy and begs her brother for help! Pietro rushes to her side and manages to catch her before she falls, but Wanda faints. The Avengers bring her to the resting rooms, where Hercules admires the devotion Pietro has for his sister. Pietro explains that’s only natural, because they have been orphans for a very long time and in the Balkans, where they used to live, decided to simply look out after each other because nobody else would. When their powers manifested, it turned out that they were actually mutants and people feared and hated them, until they became Avengers.
Hercules understands, and so does Hawkeye. He remembers the Black Widow, who also meant the world to him, and would also take care of her, much like Pietro does for his sister. He wants to know why she betrayed America the way she did and, more importantly, why him?
Meanwhile, the Black Widow has stolen a speeding plane and heads back to SHIELD, thinking this is the best way to deliver the stolen plans to them. She declares to herself that nobody, not even her beloved Hawkeye, can learn the truth about this. At the same time, soldiers report back to General Ross that the Widow has stolen their X-76 Vertical Jet. Ross has already enough problems concerning the Hulk, thinking he and the Widow must be working together. Back at Avengers Mansion, Hawkeye hopes he shall someday learn the truth about Natasha’s actions and shall be together again, only to never again depart.
Meanwhile in Atlantis, the Sub-Mariner finishes a game in an arena and wins a battle against his gladiators. They are impressed by Namor’s strength, confident that nothing can defeat him. Namor stops fighting, as he notices Vashti entering and seems to have something important to say. Vashti admits he has but it needs to be discussed in private. They move over to Namor’s computer room, where Vashti informs Namor that they’ve spotted a submarine. They don’t know the purpose of their presence but suspect a sinister motive is behind it. Namor wants to learn the truth of it, until he notices the submarine launching a torpedo, which destroys a coral reef! Namor has seen enough and swims into action.
In his fast speed, Namor notices that another missile has been launched on another reef and hopes he can prevent it from impact. He goes to sit on it though has to admit that this missile is harder to dismantle than the ones he used to destroy in the past decade. It almost seems to have a mind of its own. However, Namor refuses to give up and continues to try to dismantle the missile.
Meanwhile in the sub, the sailors and their captain have spotted Namor and recognize him. But they notice Namor doing something strange: he’s reversing the missile’s direction towards them now! They panic but the missile doesn’t hit them, but an undersea mountain as Namor intended. He hopes that by this the surface dwellers shall realize to turn back, now that they’ve still got the chance for it. Namor takes off, but the captain of the sub orders to follow him. The sailors are certain Namor meant for the missile to miss them as a warning, but the stubborn captain refuses to shout his command a second time. And he warns that he wants the Sub-Mariner alive!
Namor notices the sub following but has another plan thought up. He leads them into a rare species of seaweed, which gives the sub several electrical shocks. It’s a little damaged and the sailors report that the weed is so think they’re stuck in it. Namor triumphs though still feels a strange tingling sensation inside his head. The sailors report back to their base to come help them. Namor realizes that the sailors must be requesting for help, and he decides to follow the radio waves, which he can feel thanks to his hybrid senses, and swears that if they have bad intentions he shall destroy them no matter their number!
Back at their mansion, the Avengers are startled to have seen on TV that it now appears Captain America and the Red Skull are working together! And what’s worse, the Red Skull’s levitation ray held the entire city poised above certain doom. Hank refuses to believe Cap has turned evil, no matter what they saw. Suddenly, several flashing lights go off which means an Avenger is trying to call the mansion. Wasp goes over to the monitors, and recognizes the call coming from Cap himself! Everyone rushes towards the screens, thinking Cap might be in need of help.
Cap promises that he isn’t working with the Red Skull at all, but managed to sneak away to inform his teammates about something called the Cosmic Cube. Cap doesn’t have the time to properly explain its powers but knows that whoever possesses it has enough power to destroy the entire universe! Cap wants the team to go find the Cube and gives them its location. Then he quickly closes communication, with the Avengers thinking the Red Skull must have walked in. Hawkeye isn’t concerned, thinking Cap can handle himself. He grabs some extra arrows and Janet a supply of wasp stings. Hank smiles, as he remembers a time when Hawkeye couldn’t stand Cap and now he’s acting like a member of his fan club. Hawkeye jokes that his eyesight has been improved and knows better now.
They go check up on Quicksilver, who’s still guarding his sleeping sister. He’s confident Wanda only needs a little sleep and will be better soon, and wants to tag along on the mission. Hawkeye tells him to stay and take care of Wanda, promising they’ll do the rest. Hercules asks if he can join the heroes, which they accept. As they take of in their plane, the Avengers notice the Cub seems to be located on a Caribbean island. Hawkeye tells them they better move fast as he’s got some unfinished business to attend to, thinking to himself that means once they’ll be back he’s going to find out how to locate Natasha and go after her.
Elsewhere, outside an Army base at Puerto Nuveo, the Sub-Mariner arrives and asks the guard to step aside but he refuses. Namor doesn’t have any time to waste and slams all the soldiers out of his way, ready to storm into the base and dismantle the remaining submarines before they can enter his home and wreck it like the other one did. The Avengers arrive at the exact same spot. Hank and Wasp recognize Namor from their earlier battles and want to know what he’s doing. Namor refuses to answer and rather fights. Janet hits him with her strongest sting but Namor doesn’t even feel that.
Namor punches Janet out of his way, making Hank angry. He tries to restrain him, but Namor is stronger and throws Hank over him. He picks Hank up and heads towards the sky, where he continues to pound Hank. Hawkeye fires a lifeline arrow, which hits Namor, making him collapse. Hank and Janet land safely and Hercules throws Namor back into the ocean. He soon recovers and refuses to give up. He quickly swims back to the shore where he knocks out Hawkeye.
Hercules wants to test out his strength and Namor accepts the battle against a god. During the battle, Hercules mentions that they were merely looking for the Cosmic Cube and not for a battle, but Namor continues to battle. Hercules slams him down and once again tosses him into the ocean. Hawkeye congratulates Hercules on his victory, but Janet notices that Hank doesn’t look too happy and knows why: Namor might have known nothing about the Cosmic Cube until Hercules told him about it, meaning they could be in danger should Namor find it before they do.
Wasp’s concerns seem to be profound, as Namor orders the other sea creatures to aid him in his search for the powerful Cube. After a few hours, he notices something glowing in a deep, dark cave. It’s the Cube! Namor thinks that the Cube will give him enough strength to beat Hercules, and, at his mere thought, a waterspout helps him rise back up to shore! He is confident that this time, the Avengers shall finally fall for his might!
On shore, the Avengers have made friends with the Army and gain their assist in the search for the Cosmic Cube. Unfortunately, on that very moment, Namor returns and is ready for yet another battle. The Avengers notice him holding the Cosmic Cube, and Namor triumphs. He creates a big, green Amalga-beast, which he orders to attack his enemies. As the Army prepares for a last-ditch defense, the Avengers rush to battle Namor’s beast though they endure a hard time.
Namor faces Hercules again. This time, thanks to the Cube, Namor’s strength has increased and he seems to win. He throws Hercules into the ocean with him, where Namor is of course even stronger. However, once there, Namor has second thoughts. He doesn’t think that, with the Cube, he’ll win fairly because down here Hercules isn’t at his full strength. He thinks he better returns to the shore and orders the Cube to keep his body moist so their strength shall be equal there.
Back on the surface, Goliath manages to punch Namor’s guard out of balance and Hawkeye’s blast arrow finishes it off. Namor and Hercules continue to shore but, since they are now equally strong, neither person can defeat another. Janet thinks that, since the Cube created the Amalga-beast, it must also have the power to return to change its own form. She shrinks down to Wasp size and hits it with her Wasp-sting, making the Cube revert back to its original, tiny form!
Namor doesn’t know what hit him, but it makes him toss the cube and it falls out of his hands, into an almost bottomless crevice nearby. Namor panics and wants to go after it, but then the Army regroups and is ready to combat him. The Avengers also recover and join the Army. Namor doesn’t dare face them together –yet – and swims back into the ocean, returning back home. Once there, he thinks he needs a plan first before facing the Avengers another time, planning on using the Cube next time more carefully.
Later, deep beneath the underground, the Mole Man finds the Cosmic Cube! But, he doesn’t know what the tiny thing is all about and thinks it’s a mere lost child’s toy. Not thinking it’s a powerful weapon he can use to defeat his enemies, the Mole Man throws the Cube away and returns home.