It is often referred to as The Worst Day In Avengers History.
The story begins when the Avengers Mansion sensors warn the residing Avengers of an intruder, quickly identified as Jack of Hearts, who had died saving the life of Ant-Man's daughter Cassie Lang. Jack inexplicably detonates, killing Ant-Man (Scott Lang) in a blast that destroys half of the mansion. The Vision crashes a Quinjet onto the site, only to attack the survivors of the explosion, carrying a small army of Ultron robots which attack the survivors. During this attack, She-Hulk goes into a frenzy, resulting in her tearing Vision apart. In the aftermath of this first wave of attacks, most of the previous Avengers (even reserve members such as Spider-Man) and other heroes such as Daredevil arrive at the mansion. An enormous battlefleet of alien warships appear in the skies and begin wreaking havoc. Finally, a wounded Hawkeye sacrifices his life to save his friends by destroying an invading Kree warship.
In the end, it is revealed that the Scarlet Witch was behind these seemingly random attacks. She had been driven insane by the loss of her children years earlier; the children who actually had been magical constructs the Witch had subconsciously created from the essence of the demon Mephisto. Due to the use of her powers causing subtle 'reality warps' whenever she uses them to any great extent, continued use of her powers has driven her increasingly closer to insanity, until, finally, she has gone insane, believing that the Avengers 'took' her children away from her, and seek to do so again. In a final confrontation, the Avengers - aided by Doctor Strange - manage to stop Wanda, and she is subsequently taken away by her father Magneto, who acknowledges the mistakes he made in raising her.
A few months later, the Avengers team gather in the remains of the mansion. Quicksilver explains what has happened to his sister (the Scarlet Witch), and Tony Stark reveals that the Avengers cannot come back together due to a lack of necessary funds to repair such a high level of disaster. As the Avengers part company, they all discuss some of their favorite moments in Avengers history, such as when they first came together, when they discovered Captain America, the Kree-Skrull War, the marriage of the Vision and the Scarlet Witch, the fight with Michael Korvac, and the Ultron Unlimited crisis. As the team splits up, they are greeted by a large crowd of civilians, all of them thanking the Avengers for what they have done over the years.