In a remote universe, a solitary planet is the realm of a sophisticated society composed of hyper-evolved males, ruled by the mysterious Graydon. He sends one of these beings, known as Harold (played by Garry Shandling), on a bold adventure: to infiltrate Earth, find a human female, and successfully impregnate her before returning with the newborn.
Harold's earthly journey commences in Phoenix, Arizona, where he adopts the identity of Harold Anderson and secures a position at a local bank. Here, he encounters Perry Gordon, a charming colleague who attends Alcoholics Anonymous meetings primarily for the company rather than support. Harold joins Perry at one such gathering, where they meet Susan, a recovering addict working through her sobriety challenges.
Before pursuing his mission, Harold realizes he must first solidify his bond with Susan by exchanging vows in a Vegas wedding ceremony. As they embark on their new life together, Susan is astonished by her own joy in Harold's affections, oblivious to the fact that men from his planet differ anatomically. Harold is equipped with a prosthetic penis that emits a distinctive whirring sound whenever he becomes aroused.
However, the journey to parenthood proves to be fraught with challenges for the couple. Meanwhile, Roland Jones, an FAA employee, becomes fixated on discovering Harold's extraterrestrial secret after witnessing his odd behavior during a flight. Roland aims to be the first to reveal Harold's otherworldly identity.
The birth of their child compels Harold to abandon Susan and return to his home planet as ordered by Graydon. Yet, the guilt and inner turmoil he faces lead him to defy his superior's orders, choosing instead to return the child to Susan and revealing the truth of his intentions. Susan is left bewildered and torn between feelings of betrayal and gratitude.
In a moment of raw honesty, Harold wishes to demonstrate his alien origins, but Roland intervenes just as the revelation occurs. Rather than embracing Harold's return or forgiving his past, Susan breaks down, realizing that her life was turned upside down upon marrying an extraterrestrial being. With a heavy heart, Harold leaves, shattering the remnants of their relationship.
As they exit, Harold's confrontation with Roland unfolds like a scripted drama. Roland's smug expression revealed his confidence in having uncovered Harold's true identity as an alien. He convinces Harold to join him in addressing Susan, who still harbors doubts about Harold's nature. Yet, before they can reveal the truth, Graydon appears, ready to reclaim his subject.
A tense showdown ignites as Graydon brandishes advanced weaponry, asserting his intent to take Harold back. Showing courage, Roland fires, hitting Graydon squarely in the chest, leaving him to fall lifeless into a fountain.
As the tension dwindles, Susan steps forward, suggesting a truce and encouraging the couple to “patch things up.” With Graydon's lifeless body removed by Roland, Harold and Susan renew their vows in a heartfelt ceremony—a vision Susan had long dreamed of. The journey home is filled with reflection as Harold shares his impending call to leadership back on his planet. Yet, Susan firmly decides she won't uproot her life or friends, voicing her concerns about the complexities of the local education system.
In a moment of compromise, Harold concedes to endure the long commute, hoping to keep their love intact despite the vast distances that lie ahead.
