A strange green rocket lands on Earth and turns into a powerful green alien. The first people he meets up with are a gangster named Grogan, and his accomplices who have just robbed a bank. The alien tells them that he is from the planet Popup on vacation and has no name. Since he can do just about anything, Grogan dubs him the Impossible Man. Taking advantage of his ignorance of Earth culture, Grogan plans to use Impossible Man to rob every bank in New York. The next day, they successfully steal a large amount of cash from a city bank. The Fantastic Four are alerted to the super-powered theft by the police, and track Impossible Man and his acquaintances to a local restaurant. Completely fooled by Grogan, the Impossible Man refuses to listen to the Fantastic Four's explanation as to what is really going on. Still not wanting to listen, the Impossible Man does battle with the Fantastic Four and manages to hold them off. Knowing that sooner or later the Four will have proof that Grogan is directly responsible for the resulting bank thefts, he has the Impossible Man go to the next bank on his own. At the bank, the Fantastic Four disguise themselves as bank workers and convince the Impossible Man to find out what Grogan really thinks about him. They have to hope that the Impossible Man listens to their advice and turns against Grogan, as well as figuring out a way of getting him off the Earth before he causes any more trouble.