The Avengers, including Captain America, Iron Man, and Thor, have gathered together to consider the android Vision's application for membership. The retired Avengers have never met Vision before. Cap leads them in attacking him, to demonstrate his ability to switch between intangibility and diamond-hardness with great strength. (But not his ability to fly, walk through walls, and emit thermoscopic rays from his eyes.)
The senior three would still like to know more of Vision's origins before accepting him. But Vision can only remember that Ultron-5 claimed to have created him, and sent him against the Avengers last issue (until he rebelled).
Goliath remembers working on creating a being like Vision, a solar-powered synthozoid (humanoid with synthetic organs). But he can't remember what he did with it. So Thor flies the group (by hammer power) to Hank's abandoned suburban lab (last seen trashed by Dragon Man in #42).
Hank uses a device to stimulate his memory, and now recalls rebuilding his lab. But a crude robot he had built had achieved sentience, and wanted to kill the man it thought of as father. Failing that it had hypnotised him into forgetting the encounter, and left on a mission of self-improvement.
The Avengers now guess that the robot was the original Ultron, which must have rebuilt itself several times since then and is now incarnated as Ultron-5. And that it used Hank Pym's synthozoid experiment to create Vision.
They also find that a brain recording of Wonder Man is missing. Simon Williams had a brief super-career in #9 similar to Vision's. He was given super powers by villains (Zemo/Enchantress/Executioner) and pitted against the Avengers, but then turned on his masters. Unfortunately he died. The Avengers deduce that Ultron gave Vision Wonder Man's brain pattern.
Returning to the mansion, the Avengers accept Vision as one of themselves. The active roll-call is now Black Panther, Goliath, Hawkeye, Vision and Wasp.