Last issue Black Panther was captured by his enemy Man-Ape. But before that the villain deliberately attacked Captain America. This makes the Avengers and Captain America think Man-Ape wasn't working alone. So they have called in Iron Man and Thor as reinforcements.
While they discuss who could be behind Man-Ape, Vision dons a human disguise for the first time, to let the school where Panther teaches as Luke Charles know that he won't be coming in today. But his rubber-like mask and cold voice fluster the Principal Miss Hotchkiss.
The Avengers are right. Man-Ape is part of the Lethal Legion, with Living Laser, Power Man and Swordsman led by Grim Reaper. They all want revenge on the Avengers. Most just for previous defeats. But Reaper has his own reason.
The villains split up and leave to execute their parts of Reaper's plan, leaving Panther chained up with his friend Monica Lynne behind a force field. But the force field fails and Panther breaks his chains. Then he contacts the Avengers to tell them who their foes are, and to warn them where the Legion members have gone.
But then his contact fails, and Reaper reappears. Panther's 'escape' was all part of a plan to split the Avengers up. Those who have gone to Greenwich Village to intercept Reaper will find they are on a wild goose chase. And the Legion will be waiting for the others.
Panther and Reaper fight while the villain of course explains all that. And also reminds Panther that he blames the Avengers for his brother Wonder Man's death, as he did in T'Challa's debut issue #52. Ranting over, Reaper gasses Panther and Monica unconscious with his scythe.
Goliath and Scarlet Witch enter the water main below Avengers Mansion looking for Power man and Swordsman. Clint is still smarting after being dumped by Black Widow, and brusquely brushes aside Wanda's suggestion that he might need her help. The villains blind them with an intense beam of light (equipment courtesy of Living Laser?). Even so Goliath does well against Power Man, while the Witch holds off Swordsman. But then Clint runs into an overhead pipe, and his flailing fist knocks Wanda out. While Goliath is dazed Swordsman renders him unconscious with gas from his sword.
Captain America and Quicksilver tackle Living Laser and Man-Ape in the local power station. Man-Ape brings the stairway they are on crashing down. The ensuing battle rapidly devolves into Cap vs Man-Ape and Pietro vs Living Laser. Quicksilver easily dodges laser's blasts, but is felled by flying concrete. Cap holds his own against Man-Ape until he is smashed to the floor by a flood of pressurised water from broken hydraulic generators.
Iron Man and Thor of course went looking for Grim Reaper, and aren't seen again in this issue.
Later Reaper is gloating over Cap and the four captured Avengers dying from a slow-acting poisonous gas. Even though Swordsman reminds him that only Cap was actually an Avenger when Wonder Man died.
Then Power Man returns from Avengers Mansion with an unconscious Vision, who gets thrown into the gas tank with the rest. But he has also brought along the Avengers' personal files. And the horrified Reaper learns that Vision has Wonder Man's brain patterns. Desperate to save what remains of his brother he smashes the gas tank, releasing the Avengers.
But 'Vision' turns out to be a groggy Power Man. And Vision himself floats out of his Power Man disguise. Turning diamond hard he shatters Swordsman's sword. Cap and Pietro make short work of their erstwhile opponents. And Black Panther kicks Grim Reaper to sleep.
The issue wraps up by explaining that Panther had suspected that his earlier escape was too easy, and his message to the Avengers had included a code phrase meaning 'beware of a trap'. So the Avengers were ready when the Lethal Legion attacked them. They were never really knocked out. They allowed themselves to be captured so they could get the whole gang together.
But their plan obviously backfired when they were locked in the gas tank. Vision is the hero of the hour (even though Goliath claims they would have smashed their way out without him). So they're shocked when he declares he is quitting the team, because he feels an android doesn't belong amongst humans.