In a bygone era of turmoil, a ferocious beast lays waste to the realm dominated by King Bruno the Enigmatic. While life continues in isolated villages, in one such community, young Dennis Cooper – portrayed with an endearing naiveté – aspires to follow in his father's footsteps as a cooper, all while laboring under the critical eye of his ailing father. Unfortunately, Mr. Cooper holds a deep resentment towards his son, viewing him as unworthy due to Dennis's preoccupation with financial gain rather than true craftsmanship. As the father's illness approaches its end, he delivers a harsh condemnation, publicly disowning Dennis during a blistering deathbed rant. Heartbroken and feeling abandoned, Dennis resolves to set out for the capital city of the kingdom. His goal is to forge a new path and return to win over his unrequited love, Griselda Fishfinger. In a bittersweet farewell, as he struggles to part from an oblivious Griselda, she carelessly discards a rotten potato—something Dennis catches and treasures as a symbol of their fleeting connection.
The capital, now teeming with terrified refugees fleeing the monster's rampage, is rife with chaos. Wealthy merchants take advantage of the desperate situation, selling exorbitantly priced goods to the panicked populace. Amidst the turmoil, local craftsmen reject Dennis's attempts to improve their struggling operations, leaving him in search of both work and nourishment. Concurrently, King Bruno plots to challenge the menace with valiant knights through a grand jousting tournament to determine who is best fit for the perilous task. The outcome is vital; the victorious knight will gain the title of prince and the hand of the mysterious Princess, who waits longingly in her tower for a true hero to rescue her.
Fate intervenes as Dennis meets Ethel, the squire to the illustrious Knight of the Red Herring, who offers him a warm meal and friendship. However, miscommunications soon spiral into a series of misadventures that culminate in Dennis's abrupt exit from a tavern, where Ethel has charmed the innkeeper's wife. Seeking refuge, Dennis accidentally finds himself under the Princess's spell, as she mistakes him for a gallant prince in disguise. Intrigued by the potato, which she interprets as a romantic token, Dennis becomes bewildered and fails to set the record straight. He eventually reveals his heart's desire for Griselda, leading the Princess to release him with a heavy heart. In a surprising twist, the Princess outfits Dennis in a nun's habit, which intriguingly leads him into the midst of zealous fanatics who perceive him as the embodiment of evil or disguised Satan.
As the jousting competition reaches a blood-soaked climax, the King's chamberlain, Passelewe, grows increasingly uneasy about the ferocious battles resulting in potential casualties. He convinces King Bruno to abandon the perilous contests and opt for a less lethal challenge of hide-and-seek to crown a champion. Surprisingly, the Knight of the Red Herring triumphs in this unorthodox match. Meanwhile, Ethel's infatuation with the tavern keeper's wife positions Dennis as the new squire, although he remains oblivious to the switch.
The disaster unfolding in the city catches the eye of cunning merchants, who secretly enlist a ruthless warrior, known only as the Black Knight. He infiltrates the lair of the beast and assassinates the Knight of the Red Herring with merciless precision. As he gears up to eliminate Dennis, the dragon-like monster emerges from the shadows, compelling the Black Knight to battle for his survival. Just when it appears he has triumphed, he is ultimately toppled down a cliff by the beast’s relentless assault. In an unforeseen twist, Dennis inadvertently defeats the monster when it skewers itself on his trembling sword, subsequently severing its head in a moment of unexpected bravery. With the threat neutralized, Dennis presents the grisly trophy to King Bruno, earning him the title of hero.
As Griselda's admiration for Dennis blossoms alongside his newfound acclaim, she seems destined to accept his proposal. However, fate has a plan of its own. True to his word, King Bruno grants Dennis half the kingdom, binds him in marriage to the Princess, and sets the newlyweds adrift on an uncertain honeymoon filled with uncharted adventures.
