On Arkon's world, Thor uses his hammer to return the Avengers and their mansion to where they came from. Black Knight goes back to Stonehenge. Thor and Black Panther find themselves back in New York with the mansion. But the other four Avengers, who had been abducted with the mansion, aren't within it. Thor and Panther put off investigating to attend a scheduled children's charity event with Captain America and Spider-Man.
Goliath, Quicksilver, Scarlet Witch and Vision are intangible, and they see the world burning up due to the sun. A newspaper tells them they are a few days in the future. Wanda casts a hex which makes them real, and the world isn't melting anymore. Another paper shows they are back to the present. But they don't notice clues that they are in an alternate world.
Arriving at a somewhat different mansion they encounter a man they recognise as Nighthawk of the villainous Squadron Sinister, but he doesn't recognise them. Chasing him they meet four new characters American Eagle, Hawkeye (not our one), Lady Lark and Tom Thumb.
Vision suspects he knows what has happened. His suspicions are confirmed when a screen shows a message from the other three Squadron Sinister characters Dr Spectrum, Hyperion and Whizzer. They refer to the whole group as the Squadron Supreme, and the city the mansion is in is Cosmopolis rather than New York. The Avengers realise that they are in an alternate world.
The other three Squadron members are in Atomic City launching rocket Brain-Child 1 to gather data from the sun. The Avengers guess that this rocket might cause the disaster they saw in the future, and swear to stop it. But the Squadron members present of course fight them.
Hawkeye is an archer. Tom Thumb is a midget with lots of gadgets. American Eagle flies and is strong. Lady Lark emits a sonic cry. The Avengers defeat them, and take a jetcraft to Atomic City. They take Nighthawk with them and convince him that the sun is going to go super-nova.