In the midst of his ordinary life on Duckworld, an unexpected twist catapults Howard (Howard the Duck) into a thrilling cosmic escapade. A bizarre incident involving his armchair launches him through the cosmos, landing him in Cleveland, Ohio, where he discovers a mesmerizing blend of the familiar and the alien. His encounter with Beverly Switzler, who finds herself in a dire predicament, ignites a spark of heroism in Howard. Utilizing his unorthodox martial arts techniques, he valiantly defends her against her assailants. Following this chaotic event, Beverly graciously invites Howard to stay the night at her apartment.
The subsequent day, Beverly aims to call upon the expertise of Phil Blumburtt, hoping the scientist can assist in sending Howard back to Duckworld. However, upon realizing that Phil is just a lab assistant, Howard's hopes are dashed, leading him to accept his new life on Earth and to turn down Beverly’s help. He takes up a job as a janitor at a romance spa but eventually resigns, rekindling his bond with Beverly, who is part of the rock band Cherry Bomb.
Tensions rise when Howard bravely confronts the band’s manager, who has sinister intentions of manipulating them for profit. Although he initially triumphs, Howard soon finds himself back at Beverly’s apartment. There, she convinces him to step in as Cherry Bomb’s new manager. As their connection deepens, their romantic relationship reaches a passionate crescendo, only to be abruptly disrupted by Phil and his team, who disclose that a malfunctioning laser spectroscope brought Howard from Duckworld to Earth.
In their urgency to rectify the situation, the group visits the lab, but chaos ensues when the device fails once again, presenting a potential threat to Earth. Amidst this upheaval, Dr. Walter Jenning becomes the unwilling host to an otherworldly being, who ominously refers to himself as the Dark Overlord of the Universe. While they dine at a local eatery, the creature showcases its burgeoning mental powers by wreaking havoc on the surroundings.
A series of misfortunes befalls Howard, as his attempts to broker peace are met with animosity from truckers. He is captured and nearly meets his demise at the hands of the diner’s chef before the Dark Overlord intervenes, demolishing the establishment and abducting Beverly.
Desperate to rescue her, Howard and Phil discover an ultralight aircraft, which becomes their vehicle for the perilous quest to confront the cunning Dark Overlord and save Beverly. Meanwhile, the Dark Overlord concocts a wicked plot to transfer his essence into Beverly’s body via the dimension machine. With the fate of humanity at stake, Howard and Phil arrive just in time to thwart the malevolent plan. They initially believe they've vanquished the Dark Overlord using an experimental neutron disintegrator, but the creature’s true form emerges, forcing them into a final showdown. Undaunted, Howard fires the disintegrator again, annihilating the beast and eliminating the threat of the Dark Overlord's army. However, this decisive action results in the destruction of the laser spectroscope, their sole means of returning to Duckworld, rendering Howard’s abrupt change of fate undeniable. Consequently, he resolves to remain on Earth as Beverly's manager, while Phil embarks on her tour as part of the crew. Together, they take the spotlight, where Howard joins Beverly on stage, creating a magical combination of music and enchantment.
