When Seth Brundle makes a huge scientific and technological breakthrough in teleportation, he decides to test it on himself. Unbeknownst to him, a common housefly manages to get inside the device and the two become one.
Seth Brundle, a brilliant but eccentric scientist, meets Veronica Quaife, a science journalist, at a press event. He takes her back to his warehouse home and laboratory and shows her his invention: a set of “telepods” that allows instantaneous teleportation from one pod to another. Seth convinces Veronica to keep the invention secret in exchange for exclusive rights to the story, and she begins to document his work. Although the telepods can transport inanimate objects, they mutilate live tissue, as is demonstrated when a baboon is turned inside-out during an experiment.
Seth and Veronica begin a relationship. Their first sexual encounter inspires Seth to reprogram the telepod to cope with living tissue, and he successfully teleports a second baboon. Veronica departs before they can celebrate, and Seth worries that she is rekindling her relationship with her editor Stathis Borans; in reality, Veronica has left to confront Stathis about a veiled threat, spurred by his jealousy of Seth, to publish the telepod story without her consent. Seth decides to teleport himself alone, unaware that a housefly has slipped inside the transmitter pod with him. He emerges from the receiving pod seemingly normal.
Seth and Veronica reconcile. Seth begins to exhibit increased strength, stamina, and sexual potency, which he believes is a result of the teleportation “purifying” his body. He has sugar cravings and Veronica is concerned about Seth’s insanity and strange, bristly hairs growing from his back. He becomes arrogant and violent, insisting that the teleportation process is beneficial, and tries to force Veronica to undergo teleportation. When she refuses, he abandons her, goes to a bar and partakes in an arm-wrestling match, leaving his opponent with a compound fracture. He meets a woman named Tawny and brings her back to his warehouse, where Veronica rescues her from teleportation. Seth throws Veronica out, but when his fingernails begin falling off, he realizes something went wrong during his teleportation. He checks his computer’s records and discovers that the telepod computer, confused by the presence of two lifeforms in the sending pod, merged him with the fly at the molecular-genetic level.