The first arc to follow Waid's "Imaginauts" arc was the "Unthinkable" arc. This arc would pave the way for the next two crucial arcs, in this triple threat, Authoritative Action" and the "Hereafter Arc" all in the main Fantastic Four comic.
"Unthinkable" deals with the ramifications of Doom's delivery of Valeria Richards. Unknown to the team, Doctor Doom used the opportunity to cast a spell on the baby to make her into his magical familiar. The Fantastic Four had no idea of this until Valeria seemingly spoke her first word, "Doom". In that instance Doom carried out a devastating blow on the team. A trio of demons, whom Doom made a deal with, kidnapped Franklin and took him to hell.
In the struggle, both Reed and Johnny tried in vain to rescue Franklin but the demons were too powerful. They sent a barrage of demon fire towards the Human Torch and thus burnt him in the process. A surprised Johnny exclaiming how he'd never been burnt since he got his powers. At the same time, Sue and Ben were rushing towards Reed's lab to tell him of what just happened to Valeria, then learn what happened to Franklin. Understandably distraught and seeing a connection between Valeria's first word and the sudden attack they deduce that Doom was behind the attacks.
They travel to Latveria hoping to find Franklin and fix what was wrong with Valeria. As they headed into Latveria Doom had placed several Doombots and copies of himself, to trick the team. The Doombots were easily taken care of. When Sue finally thought she'd gotten Doom, she attacked him with a devastating attack, only to realize too late it wasn't the right Doom. Doom was hiding and finally made himself known. He cast his magic on the team and then teleports baby Valeria into his arms, seemingly winning this encounter with the team.
He takes them back to his castle where he uses his magic to have the team suffer through painful versions of their team member's powers, and trying to demoralize them in a different way. He gave Johnny, Reed's signature stretching powers and tried stretching him to his limits. At the same time, he gave Sue a painful version of Johnny's flame power. Ben was forced to fight monster after monster. But he left the most "cruel" fate for Reed. Both Doom and Reed realized that Reed's understanding of magic has always been flawed. So Doom stuck him in a library filled only with magical literature making Reed feel useless.
As Reed sits in the room one of the magical books topples over and he notices a message written in flames that says "Science is everything." He opened the book to find the astral projection of Doctor Strange who had been imprisoned by Doom. Together, Dr. Strange tried in vain to teach Reed magic. To help understand and let go of his analytical mind while practicing magic. Reed feeling useless, was going to give up until he realized something that would help him develop a bit of innate magical abilities. He swallows his pride and admits not to understand it and he uses that to fuel him. He manages to escape and returns to Castle Doom. He defeats Doom and rescues his teammates.
The team quickly hurries to find Franklin, seeing him in Hell in the middle of the group of demons who had taken him. Franklin had escaped momentarily before but had been found again. The team battled the demons, and later find that Doom hadn't been completely defeated. Once again, Reed puts an end to Doom, this time the Demon taking possession of Doom for the fact that he didn't come through with his part of the deal (delivering Franklin) and he's thrust into Hell. But before he leaves, he badly scars Reed's face.
This arc would led into the actions of the next arc, "Authoritative Action".