WARNING: The following contains major spoilers for Fantastic Four: Road Trip #1 by Christopher Cantwell, Filipe Andrade, Chris O'Halloran, and VC's Joe Caramagna, on sale now.
Marvel's premier super family, the Fantastic Four, have a little downtime to spend together without having to save the world, or some other world. The rare chance at a normal vacation is jumped at by the gang, and Reed decides that a classic road trip is the best idea. Driving through the Arizona desert on their way to the Grand Canyon, the family expects a boring getaway at the worst. Of course, things are never that simple, and a classic Fantastic Four villain is taking the opportunity to show the Richards clan that he isn't a joke anymore.
Reed Richards, to the rest of the family's displeasure, suggests they make a quick stop at a meteor crater that they'll be passing on the drive. The rest of them begrudgingly humor the patriarch of the family, whose curiosity has been piqued by the strange energy signature of the soil in the crater. Reed is hoping that they can bring a large sample of the soil to their cabin, and enlists Franklin to act as a shovel of sorts. Annoyed, but willing, Franklin whips up a whirlwind and pulls soil deep under the crater to the surface. Once arrived, Reed sets off to the lab almost immediately to begin his studies, staying up late into the night going over the soil samples.
The next day, Reed chooses to stay behind and continue his work while Ben takes Alicia for a hike and Sue and Valeria go kayaking. Reed, having gone back down to the basement laboratory, comes to the conclusion that the soil they've recovered is tainted with that from an alien world, specifically the toxic planet Spyre. Someone laid a trap for them, and Reed took the bait, leaving the entire family poisoned. As the family's powers and bodies deteriorate at an alarming rate and in particularly gruesome ways, a demented figure gloats over their impending demise, watching through a series of monitors not too far away. The Mad Thinker has returned, and he's no longer the joke villain he used to be.
A genius by any measure, the Mad Thinker was first introduced in 1963's The Fantastic Four #15. Created by Stan Lee and Jack Kirby, the Mad Thinker used his incredible prowess with statistics and probability to calculate precisely the right times to commit crimes, selling his talents to various other criminals. A paranoid belief that the Fantastic Four were the only heroes capable of ever stopping him, he began a crusade against them, even becoming successful in disbanding the team before they would eventually put an end to his scheme.
He would go on to torment the Fantastic Four many times throughout the years, but his obsession would become more of a hinderance than anything else. While Johnny and Ben were hunting the multiverse for Reed and Sue, the Mad Thinker took the team's absence as a sign that he should be their successor, forming his own Fantastic Four and failing to eliminate the originals. After chasing Johnny and Ben to a desolate alternate world, the Mad Thinker would be stranded there, before a benevolent Reed took it upon himself to rescue the villain. Now, that decision seems to be backfiring in the worst way.
Of course, the heroes are able to undo the damage that has been inflicted upon them, and come together to defeat the Mad Thinker once they've recovered. This doesn't make the villain's reappearance any less dramatic, though, as this is a sharp turn from the typically subdued and stoic Mad Thinker of days past. Maybe the time on a ruined world has changed him for the worse, or maybe so much time spent as more joke than threat finally made him snap. Either way, the brutality shown by him in this encounter certainly puts the Mad Thinker higher on the Richards' list of threats than he's ever been before.