Professor Farnsworth invites the employees of Planet Express to see his new invention: the Fing-Longer, an index-finger-extending glove. As he tries it out, it activates a TV-like device. When Fry questions the Professor regarding what it is, he explains that it is the "What If" Machine, a device that allows the user to view a simulation of a short hypothetical scenario after the user asks it a 'what-if' question. The Professor then invites the crew to try out the What-If machine.
Bender jumps at the chance and asks the What-If machine what would happen if he were 500 feet tall. The simulation begins with the giant Bender being built by hundreds of smaller Benders. He flies and crashes onto Central Park and meeting with a recently unfrozen Fry. After some friendly Frisbee fun, the military is sent to deal with him.
Bender begins to wreak havoc upon New New York. To combat Bender, the Professor uses his enlarging-ray upon a hapless Dr. Zoidberg, enlarging him, only to see him wreak havoc as well, interrupted only by Bender who isn't pleased with Zoidberg destroying 'his' city. The two start to fight and Bender appears to win by pushing Zoidberg into a stadium of boiling water.
While Bender laughs in triumph, he is distracted by Fry. An enraged Zoidberg rises out of the water and snaps off Bender's feet. This causes him to fall on the Empire State Building, which appears to stab him. A tearful Fry admonishes the citizens of New New York City about the tragedy of Bender's death, whose final words lament about his inability to fulfill his purpose, which is to kill all humans. The scenario then ends.
The Professor asks Leela to try out the What-If machine. Leela initially declines, but at the prompting of Fry, Leela decides to ask what would happen if she were a little more impulsive.
The scenario starts at Planet Express, where Leela shows off her new boots bought on impulse, the only difference being a green stripe down the side. The Professor summons Leela to tell her that she is to be made his sole heir as she is so "unimpulsive" -- only to be kicked by Leela into a pit containing his man-eating anteaters, where he is promptly devoured. She tries acting like nothing's happened but Hermes finds that the Professor was murdered, so Zoidberg takes up detective work. As Hermes discovers her role in the death in a video will, she is forced to silence him by chopping him up and plunging his remains down the drain. She impulsively kills Bender using a microwave with a broken frame in order to keep him from blackmailing her about the deaths, and makes him into a cart to "hide the corpse". Amy makes fun Leela, so she is murdered as well.
Zoidberg summons the rest of the Planet Express crew into the Accusing Parlor in order to solve the murders. While Zoidberg reveals clues, Cubert, Scruffy and even Nibbler attempt to implicate Leela, only to be slain by her when she turns off the lights. Zoidberg finds a letter from recently deceased Bender about the identity of the murderer but is interrupted by Fry who leaves due to boredom; Leela kills Zoidberg as well, eating him. When Fry finally figures out the next day that she was responsible, Leela is forced to do something really impulsive: sleep with him to keep him quiet. Fry declares that he likes the new, impulsive Leela. She then ominously asks Fry to turn off the lights. Fry does so and promptly begins screaming — and then says that he really likes her.
After being told that Bender's scenario would not be done again, Fry asks what would happen if he had not "fallen into the freezer-doodle and come to the future-jiggy". The scenario starts with Fry narrowly missing falling into the cryogenic tube, and a rift in the space-time continuum appears, which shows the Planet Express crew in the future wondering what is causing the rift, and Fry horrified at seeing monsters.
After Fry explains what happened the previous night at Applied Cryogenics, the Vice Presidential Action Rangers determine that Fry was supposed to die and try to kill him, only to be proven wrong when another rift appears during the attempted murder. Nichols then suggests that Fry be frozen and Gygax gives Fry his +1 mace for protection against drunken robots in the future. Just before Fry freezes himself, he smashes the cryogenic tube, causing the universe to collapse into a space-time rift. This results in Fry and the Vice Presidential Action Rangers appearing at some other indeterminate dimension which is not part of the universe. The scenario ends with them playing Dungeons & Dragons for the rest of eternity, or at least the first quadrillion years of their imprisonment there.
After the end of Fry's scenario, the Professor curses the What-If machine for simulating scenarios even he found preposterous and dumped it into the trash can. He promptly judges the Fing-Longer to be a rousing success and is congratulated by the crew. We find out that everything before was just a simulation by the What-If machine when the professor asked what would have happened if he had invented the Fing-Longer, leaving him to lament about the possibilities if he had invented it.