After Thor returns Loki to Asgard, Earth is left with a lot of cleaning up to do. New technologies arise and with them new evils. Iron Man confronts The Mandarin and many other foes. Thor would assist if only he weren't busy taking on Malekith and Kurse in the the Dark World. Captain America is also busy adjusting to the new world which is hard when adversaries from his past keep popping up, namely the Winter Soldier.
All the while, the universe is expanding. Janet Van Dyne confronts Stark about the well being of her colleague Henry Pym. Stark Industries is a major competitor in the fields of artificial intelligence and miniaturization, fields which Pym specializes in. Pym finds himself in over his head working for Advanced Idea Mechanics, run by the mysterious Arnim Zola.
Beyond the trials of Earth, a man by the name of Peter Quill and an unlikely band of heroes confront an interstellar danger, The Magus and his Universal Church of Truth. Whose faith threatens to destroy the fabric of the universe. When the threat proves too great, they must call upon the assistance of a Mad Titan. Sealing the fate of their inevitable doom.
On Earth, through a miscalculation and an unstable power source, an overwhelming evil is unleashed indirectly by Henry Pym's own hand. Together with Thor, Iron Man, Captain America and The Hulk he must assist in the defeat of his own creation, the machine known as Ultron, which has been reprogrammed to destroy The Avengers.
Soon after, he becomes Ant-Man, a hero. Though he is troubled and wracked with guilt over his failed creation. Through a series of identity crises and dangerous experiments taking him to the worlds beneath our feet, Ant-Man becomes a superhero.
After Ultron's defeat, the glowing red power source used in it's creation catches the eye of a cosmic presence...