History of the new "Doctor Strange in the Multiverse of Madness"
America Chavez and a version of Stephen Strange are chased by a demon in the space between universes while searching for the Book of Vishanti. That Strange is killed and Chavez accidentally creates a portal that transports herself and Strange's corpse to Earth-616.
Meanwhile, it has been 5 months since Ben and May have been born, and Peter is being both a good husband to MJ, and a good father to Ben and May, and at the same time continuing being the Amazing Spider-Man, (through he does so a bit less than before because he wants to be a good husband and a good father, and so he concentrates more of his time being Peter Parker, through he still finds time being Spider-Man), and Peter is passing time with his family, when he sees a portal opening in the living room, and through that portal, they see collapsing America Chavez, full of injuries. Peter and MJ medicate her, and when she wakes up, she explains what has happened to her, and that these demons are chasing her because she has the power to travel through the multiverse.
Peter brings America Chavez to the Sanctum Sanctorum, where he meets Doctor Strange, and his friend Ned, that now is a powerful sorcerer, married to Betty Brant, and with childs of his own. Peter explains Chavez's situation, when a demon attacks the Sanctum Sanctorum, but Strange defeats it. Recognizing witchcraft runes, Strange decides to consult Wanda Maximoff for help.
Meanwhile, Wanda, Pietro, Billy and Tommy (that have recently started their carreer as superheroes) have defeated Agatha Harkness, and Wanda destroys the Darkhold, while she sends Agatha, now without her powers, to justice. Strange, after congratulating Wanda for her victory, he consults her, and asks her for help. On the Sanctum Sanctorum, Wanda investigates the runes of the demon, and she realizes, to her own shock, that this magic is hers, yet she knows she has not done it. So they decide to go to Kamar-Taj to investigate more.
Kamar-Taj is suddenly attacked, and Strange sees that the attacker is another version of Wanda. Wanda reveals that she comes from the original timeline, the Darkhold had saved her from the spell of the original Strange, but she's not interested in bringing the old world back. She wants something else. She has observed, in these many years, what Peter has done. Seeing that a man, that was destined to remain alone, just like her, instead got a second possibility, and got his happy ending, so she has decided to get for herself the happy ending she deserves.
After acquiring the Darkhold and becoming the Scarlet Witch, Maximoff believes that controlling Chavez's powers will allow her to reunite with Billy and Tommy, the children she created during her time in Westview, but Strange refuses to surrender Chavez. So Maximoff attacks Kamar-Taj, killing many sorcerers. Chavez accidentally transports herself, Wanda and Strange to Earth-838 while Maximoff uses the Darkhold to "dreamwalk", taking control of her Earth-838 counterpart, who lives a suburban life with her own Billy and Tommy. ( The reason why she can't get contol of 616 Wanda, it's because Billy and Tommy, during one of her birthdays, gave her a necklace, which in reality is a powerful artifact that protects her from the powers of the Darkhold) A surviving sorceress sacrifices herself to destroy the Darkhold and break the dreamwalk. Enraged, Maximoff forces Wong to lead her to Mount Wundagore, the source of the Darkhold's power, to reestablish the dreamwalk.
While searching for help, Strange, Wanda and Chavez are apprehended by Earth-838's Sorcerer Supreme, Karl Mordo, and brought before the Illuminati, a group consisting of Mordo, Peggy Carter, Blackagar Boltagon, Maria Rambeau, Reed Richards, and Charles Xavier. They explain that through reckless use of their universe's Darkhold in an attempt to defeat Thanos, Earth-838's Strange triggered a universe-destroying "incursion". After defeating Thanos, the Illuminati executed their Strange to prevent him from causing more harm. Mordo believes that Earth-616's Strange is similarly dangerous, but Maximoff reestablishes her dreamwalk at Mount Wundagore and arrives in her Earth-838 counterpart's body before they can pass judgment. She kills all of the Illuminati except Mordo, whom Strange subdues before fleeing with Chavez. The two escape with help from the Earth-838 counterpart of Strange's ex-fiancé, Christine Palmer, a scientist working with the Illuminati.
Strange, Chavez, Wanda and Palmer enter the space between universes to find the Book of Vishanti, which is the antithesis to the Darkhold, but Maximoff appears and destroys it. She then takes over Chavez's mind, using her powers to send the others to an incursion-destroyed universe. Strange defeats the destroyed universe's Strange, who has been corrupted by his universe's Darkhold, and uses it to dreamwalk into the body of his deceased counterpart on Earth-616. With Wong's help, Strange saves Chavez from Maximoff as she tries to take Chavez's powers, and encourages Chavez to use her abilities. She transports Maximoff to Earth-838, where she sees Billy and Tommy recoil from her in fear while crying for their real mother. Realizing the error of her ways, Maximoff relents and uses her powers to bring down Mount Wundagore, simultaneously destroying all copies of the Darkhold throughout the multiverse. Strange sees Maximoff unconscious, but still alive, and, after returning to his own body, Chavez returns Strange, Wanda and Palmer to their respective universes.
After Wanda does to Maximoff the same magic she has done to Agatha, Chavez send Maximoff, on a non-return trip, to a universe where Billy and Tommy are orphans.
Sometime later, Kamar-Taj is repaired and the surviving sorcerers, joined by Chavez, continue training. Strange develops a third eye as a result of using the Darkhold and dreamwalking into a corpse.