The Invasion Of The Lava Men The Avengers return to their mansion to inspect the damage caused by the battle with the Hulk. They disband for the time being and Captain America teaches Rick Jones some acrobatic maneuvers.
Days later, a mysterious high-pitched sound destroys a computer in one of Tony Stark's Long Island factories and Iron Man is informed. Meanwhile, Giant-Man and the Wasp are conducting experiments inside a large anthill. They are also affected by the noise and escape before the anthill collapses. In his medical office, Don Blake reads about the effects of the noise in the newspaper. Thor meets Captain America and Rick Jones, who are still training, and they witness another shockwave. The six heroes investigate the source of this new unknown threat.
Meanwhile, in an army base in the west of the country, a strange rock breaks the surface of the earth and the soldiers investigate. Overseeing the events is General Thaddeus "Thunderbolt" Ross. They are interrupted by his daughter Betty, accompanied by Bruce Banner. Banner is deep in thought, mentally reliving the accident that changed him into the Hulk, as well as battling against his former allies the Avengers. His daydream is broken by General Ross, who demands that Banner investigate the giant rock. Banner deduces that the rock is actually being pushed to the surface by something underneath.
Beneath the ground, it turns out that Banner was correct. The Lava Men have created a machine that slowly pushes the "living rock" to the surface. Molto, one of the Lava Men, pleads with Basallo, the king of the Lava Men. Molto wishes for the Lava Men to stop raising the rock, as the humans are not evil and do not deserve this. He is however struck down by Jinku, the Lava Man witch doctor, and accused of cowardice because of his defeat by Thor.
Back on the surface, the army is about to destroy the rock with missiles when the Avengers arrive. Iron Man tries to cut through the rock, only to discover it is actually alive. He blasts underneath the rock to see what is below it and stumbles across some Lava Men. They overwhelm him with sheer numbers and begin to overheat his armor. At the last minute, Iron Man is saved by Thor and Captain America. Due to his immortality, Thor decides he is the only one that can continue. As he approaches, the Lava Men melt the earth below him, changing it into lava. Thor casually walks through it, to the Lava Men's amazement. Thor finds Basallo and Jinku, and demands that they stop raising the rock. Basallo explains the origin of the rock and that if anybody attempts to destroy it, it will explode with tremendous power. Their only hope is to push it to the surface before it explodes so that it will only destroy the surface life and not the entire planet. Thor tries to think of a way to save both the planet AND the life on the surface.
The Lava Men attempt to invade the surface and come face to face with Captain America. He fights bravely but is stopped when the Lava Men bind him with cinders. Rick Jones rushes to his aid and begins to break Cap free while Iron Man faces the Lava Men.
Elsewhere, Giant-Man and the Wasp have been analyzing the living rock and they find a patch that isn't pulsating. If this spot is struck with enough power, it should cause the rock to implode, rather than explode. They rush to find Thor and find Iron Man, Captain America and Rick Jones. Giant-Man lifts the Avengers' helicopter and blows back all the Lava Men with the spinning rotors. Rick Jones finally sets Cap free and they travel underground to find Thor.
Back on the surface, Bruce Banner is still carrying out his research when he turns into the Hulk. He hears the voices of his enemies, the Avengers, and proceeds towards them. The Avengers panic and try to lure Hulk away from the living rock. Thor attempts to join in the fight but is ambushed by Jinku. He points his witch doctor's rod at Thor and miraculously changes him back into Don Blake, as well as causing the tunnel to collapse. He flees, thinking that Thor is bewitched and able to change his form, leaving Blake injured in the rubble.
On the surface, the rest of the Avengers attempt to deal with the Hulk. Cap, Giant-Man and the Wasp have a plan. Using their growth capsules, Giant-Man and the Wasp taunt and tease the Hulk, luring him onto the living rock. They take him to the correct spot to strike and coax him into striking it, causing the living rock to implode.
Underground, Don Blake uses the last of his strength to change back into Thor as the tunnel completely caves in around him. He breaks free and confronts the Lava Men, convincing them to stop their invasion and to return to their own land.
Outside, General Ross declares the threat to be over and Betty rushes off to look for Bruce, finding him injured, but alive. As the Avengers leave, they receive a "condition red" distress call from the Teen Brigade.
