An old gypsy, Django Maximoff, uses his magic stone to steal the spirits of Quicksilver and the Scarlet Witch, and place them inside little wooden dolls. He claims that he is their father, and that their real names are "Ana" and "Mateo," although the mutant twins have long believed themselves to be the children of Golden Age heroes, the Whizzer and Miss America. The Avengers locate him and the Vision destroys the stone, restoring the twins' spirits to their normal bodies. To investigate Django's claims about their origin, the twins take a leave of absence from the Avengers and accompany the old man back to their native country of Transia.
On their first night, the sorcerer Modred shows up at Wanda's room and offers his help in her quest for her identity. He takes her to Wundagore Mountain, and prepares her as a host of the evil god Chthon. Quicksilver finds Bova, who tells him of their origin: they are the twin son & daughter of Magda, a woman that fled from her husband and sought refuge in Transia. She gave birth, and then escaped, fearing that her husband may find her and take her children. Bova tried to give them to the Whizzer (who was there with Miss America at the moment, and whose child died during birth), but he fled, distraught over the death of his child. The High Evolutionary gave them instead to a Gypsy family who lost their kids Ana and Mateo. Now Quicksilver knows everything... except the identity of his father.
Wanda is finally possessed by Chthon, and the Avengers show up. The Beast manages to steal the Darkhold and break the spell, and Quicksilver manages to use the wooden doll to trap Chthon's spirit and free Wanda. He then threw it into the abyss, and Wanda unleashes a mountain slide over it. The end.
The Yesterday Quest provides examples of:
- Arc Welding: Mark Gruenwald and his collaborators used this story to explain and reconcile all the conflicting stories about Pietro and Wanda's childhood and origin, and to explain or wrap up plot points from other series such as Modred's short-lived series in "Marvel Chillers."
- Big Bad Wannabe: For all his set up and bravado, Chthon was easily defeated in a pair of swift movements. His servant Modred was a higher menace than him.
- Bystander Syndrome: Gyrich was perfectly fine leaving Transia at the mercy of an evil god, as long as the menace stays far away from the United States.
- Combat Pragmatist: Modred is a better sorcerer than the Scarlet Witch, but she can still best him. There are other ways, such as... a good punch!
- The Cuckoolander Was Right: Initially, Django seems like just a senile old man with a misplaced fatherly love for Quicksilver and the Scarlet Witch. Eventually, he is proved right.
- Demonic Possession: The evil god Chthon possessed Wanda.
- Dude Looks Like a Lady: Chthon is a male god, but he has no problem possessing the Scarlet Witch's body and keeping her costume (see the main picture; the one at the left is Chthon). Modred still calls him "My Lord", despite his female appearance.
- Everything Trying to Kill You: Once Chthon possessed Wanda, the forest became a really dangerous place.
- Female Angel, Male Demon: The Scarlet Witch and Chthon verge into this.
- Obstructive Bureaucrat: Gyrich, who was installed at the Avengers Mansion at the time. Initially, he refused to let the team go to a foreign country, and then told the Vision that he had to leave the fate of his wife in the hands of others because... bureaucracy.
- Origins Episode: The long awaited origin story of Quicksilver and the Scarlet Witch. Only Wolverine beats them in the amount of time between premiere and full origin story.
- Refused by the Call
- The Vision could not go to Transia to save his wife. Gyrich was in the Avengers Mansion, and it's his turn to be on monitor duty, so bad luck.
- Quicksilver is not allowed to go to Wundagore Mountain with Modred and his sister: it's a dangerous path, only for those trained in arcane arts.
- That Man Is Dead:Chthon: There is no Ana Maximoff! There is no Wanda Frank! There is only Chthon!
- Tome of Eldritch Lore: The Darkhold, the book to summon Chthon.